R.

Journal of Medical
Mittal and others Microbiology (2015), 64, 1103–1116 DOI 10.1099/jmm.0.000155

Review Current concepts in the pathogenesis and

treatment of chronic suppurative otitis media
Rahul Mittal,1 Christopher V. Lisi,1 Robert Gerring,1 Jeenu Mittal,1
Kalai Mathee,2 Giri Narasimhan,3 Rajeev K. Azad,4 Qi Yao,1
M’hamed Grati,1 Denise Yan,1 Adrien A. Eshraghi,1 Simon I. Angeli,1
Fred F. Telischi1 and Xue-Zhong Liu1
1
Correspondence Department of Otolaryngology, University of Miami Miller School of Medicine, Miami, FL, USA
Xue-Zhong Liu 2
Department of Human and Molecular Genetics, Herbert Wertheim College of Medicine,
xliu@med.miami.edu Florida International University, Miami, FL, USA
3
Bioinformatics Research Group (BioRG), School of Computing and Information Sciences, Florida
International University, Miami, FL, USA
4
Department of Biological Sciences and Mathematics, University of North Texas, Denton, TX, USA

Otitis media (OM) is an inflammation of the middle ear associated with infection. Despite
appropriate therapy, acute OM (AOM) can progress to chronic suppurative OM (CSOM)
associated with ear drum perforation and purulent discharge. The effusion prevents the middle
ear ossicles from properly relaying sound vibrations from the ear drum to the oval window of the
inner ear, causing conductive hearing loss. In addition, the inflammatory mediators generated
during CSOM can penetrate into the inner ear through the round window. This can cause the
loss of hair cells in the cochlea, leading to sensorineural hearing loss. Pseudomonas aeruginosa
and Staphylococcus aureus are the most predominant pathogens that cause CSOM. Although
the pathogenesis of AOM is well studied, very limited research is available in relation to CSOM.
With the emergence of antibiotic resistance as well as the ototoxicity of antibiotics and the
potential risks of surgery, there is an urgent need to develop effective therapeutic strategies
against CSOM. This warrants understanding the role of host immunity in CSOM and how the
bacteria evade these potent immune responses. Understanding the molecular mechanisms
leading to CSOM will help in designing novel treatment modalities against the disease and
hence preventing the hearing loss.

Introduction middle ear looks red and inflamed with purulent discharge
in CSOM patients (Figs 1 and 2). It is one of the most
Otitis media (OM) refers to a group of complex infectious
common chronic infectious diseases worldwide especially
and inflammatory diseases affecting the middle ear
affecting children (Roland, 2002; Verhoeff et al., 2006).
(Dickson, 2014). OM in general is very common, as studies
Hearing impairment is one of the most common sequelae
show that around 80 % of children should have experi-
of CSOM (Aarhus et al., 2015). The resultant hearing loss
enced at least one episode by their third birthday (Teele
can have a negative impact on a child’s speech develop-
et al., 1989). OM has been broadly classified into two
ment, education and behaviour (Olatoke et al., 2008;
main types, acute and chronic. Acute OM (AOM) is
Khairi Md Daud et al., 2010). Mortality due to compli-
characterized by the rapid onset of signs of inflammation,
cations of CSOM is typically higher than other types of
specifically bulging and possible perforation of the tympa-
OM (Yorgancilar et al., 2013a; Qureishi et al., 2014). Intra-
nic membrane, fullness and erythema, as well as symptoms
cranial complications like brain abscess and meningitis are
associated with inflammation such as otalgia, irritability
the most common causes of death in CSOM patients
and fever (Pukander, 1983; Harkness & Topham, 1998).
(Dubey et al., 2010; Chew et al., 2012; Sun & Sun, 2014).
Despite appropriate antibiotic therapy, AOM may progress
to chronic suppurative OM (CSOM) characterized by per- In this article, the recent scientific advancements in epide-
sistent drainage from the middle ear associated with a per- miology, microbiology, pathogenesis, treatment and effect
forated ear drum (Wintermeyer & Nahata, 1994; Harkness of CSOM on hearing loss are reviewed. There are only a
& Topham, 1998). When examined by otoscope, the few studies available in relation to understanding the

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Mittal and others Microbiology (2015), 64, 1103–1116 DOI 10.1099/jmm.0.000155

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R. Journal of Medical
Mittal and others Microbiology (2015), 64, 1103–1116 DOI 10.1099/jmm.0.000155

(a) (b)
Inner ear Middle ear Outer ear Inner ear Middle ear Outer ear

Semicircular Bones of the Semicircular

canals middle ear Bones of the
canals middle ear
Incus
Stapes Malleus Incus
Stapes Malleus

Cochlea Cochlea
Eardrum
Ear canal Eardrum

Eustachian tube
Eustachian tube Ear canal

Fig. 1. Schematic representation of the ear under normal and CSOM conditions. (a) Under normal conditions, the middle ear
cavity is clear and empty. (b) In contrast, the middle ear becomes red and inflamed with the presence of fluid under CSOM
conditions. The red colour denotes inflammation, while yellow indicates fluid during CSOM.

pathogenesis of CSOM (Table 1). The present review is been estimated that there are 31 million new cases of
intended to draw the attention to the fact that there is an CSOM per year, with 22.6 % in children less than 5 years
urgent need to conduct studies on the pathogenic mechan- old (Monasta et al., 2012). The populations with the highest
isms of CSOM in order to identify novel therapeutic targets reported prevalence of CSOM are the Inuits of Alaska,
beyond the antibiotic therapy. A better understanding of Canada and Greenland, American Indians and Australian
the underlying mechanisms and, ultimately, the discovery Aborigines (7–46 %) (Bluestone, 1998; Coates et al., 2002;
of more effective therapies would result in decreased Couzos et al., 2003). Intermediate prevalence has been
healthcare costs and improved quality of life for CSOM reported in the South Pacific Islands, Africa, Korea, India
patients. and Saudi Arabia, ranging from 1 to 6 % (Rupa et al.,
1999; Zakzouk & Hajjaj, 2002). A prospective population-
based longitudinal cohort study among children aged 0 to
4 years demonstrated a cumulative incidence rate of
Incidence and epidemiology CSOM of 14 % in Greenland (Koch et al., 2011). However,
CSOM usually develops in the first years of life but can per- earlier studies have reported CSOM incidence rates of 19
sist during adulthood. The disease affects 65–330 million and 20 % among Greenlandic children aged 3–8 years (Ped-
people worldwide, mainly in developing countries. It has ersen and Zachau-Christiansen, 1986; Homøe et al., 1996).

(a) (b)

Perforation

Purulent
drainage

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Mittal and others Microbiology (2015), 64, 1103–1116 DOI 10.1099/jmm.0.000155

Fig. 2. Otoscopic examination of the ear. (a) A normal ear from a healthy individual shows an intact eardrum and no fluid.
(b) In CSOM patients, there is tympanic membrane perforation and purulent discharge.
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 CSOM: pathogenesis, treatment and hearing loss

These studies show that CSOM is highly prevalent in Green-

Paparella et al. (1984); Kolo et al. (2012); Luntz et al. (2013); Aarhus et al. (2014)
landic Inuits and appears very early in life, on average before
1 year of age. The risk factors that predispose children to
CSOM in Greenland include attending childcare centres,
having a mother who reported a history of purulent ear
discharge, having smokers in the household, a high burden
Saunders et al. (2011); Lampikoski et al. (2012); Kaya et al. (2013);
of upper respiratory tract infections and being Inuit (Koch
et al., 2011). Although CSOM is still prevalent in developed
countries, very few studies are available regarding this dis-
ease. The exact incidence of CSOM in the USA is not well
documented: 70 % of US children have at least one acute
middle ear infection before 3 years of age, constituting a
References

major risk factor for the development of CSOM (Kraemer

et al., 1984). In the USA, CSOM has been documented to
Khosravi et al. (2014); Gu et al., (2014)

occur most often in certain ethnic groups, with an estimated

prevalence of 12 % in Eskimo and 8 % in American Indian
children and less frequently in the white and black popu-
lation (Fairbanks, 1981; Kenna et al., 1986). For the latter
Yorgancilar et al. (2013a, b)

two groups, the exact incidence has not been documented.

It has been observed that males and females are equally
Varshney et al. (2010)

affected, but the cholesteatomatous form is more common

Elmorsy et al. (2010)

among males (Matanda et al., 2005). Additional epidemiolo-

gical studies are required to highlight the incidence of
Si et al. (2014)

CSOM in developed countries.

Microbiology
Increased transcript and protein levels of TNF-a, IL-6, IL-1b and IFN-c inflammatory cytokines

The most common cause of OM is bacterial infection of the

middle ear. AOM is predominantly caused by Streptococcus
pneumoniae, Haemophilus influenzae and Moraxella catar-
rhalis (Sierra et al., 2011; Qureishi et al., 2014). However,
Pseudomonas aeruginosa and Staphylococcus aureus are the
most common aerobic microbial isolates in patients with
Increased levels of IL-8 chemokine in middle ear effusion of CSOM patients

CSOM, followed by Proteus vulgaris and Klebsiella pneumo-

niae (Table 2) (Sattar et al., 2012; Aduda et al., 2013;
Prakash et al., 2013). A number of studies from different
countries including India, Nepal, Singapore and Nigeria
have reported that P. aeruginosa is the most common
pathogen that causes CSOM, followed by S. aureus (Yeo
et al., 2007; Sharma et al., 2010; Dayasena et al., 2011;
Table 1. Pathophysiological findings in CSOM patients

Madana et al., 2011; Afolabi et al., 2012; Ahn et al., 2012;

Biofilm formation in the middle ear of CSOM patients

Asish et al., 2013). However, studies from Pakistan

in the middle ear mucosa of CSOM patients

(Gilgit), Iran and Saudi Arabia reported S. aureus as the

most predominant pathogen, followed by P. aeruginosa
(Ettehad et al., 2006; Mariam et al., 2013; Ahmad et al.,
2013; Ahmed et al., 2013). The difference in the various
studies could be due to the differences in the patient popu-
Hearing loss in CSOM patients

lation studied and geographical variation. A cross-sectional

Ossicular chain disruption

study of bacterial microbiota in middle ear, adenoid and

Temporal bone erosion

tonsil specimens from a paediatric patient with chronic

serous OM utilizing 16S rRNA gene-based pyrosequencing
analysis revealed Pseudomonas spp. as the most common
pathogen present in the middle ear, whereas Streptococcus
spp. dominated the tonsil microbiota at relative abundance
rates of 82.7 and 69.2 %, respectively (Liu et al.,
Findings

2011). On the other hand, the adenoid microbiota was

dominated by multiple bacteria including Streptococaceae,

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R. Mittal and others

Table 2. A list of micro-organisms isolated from CSOM patients

Organisms Percentage isolation References

Aerobic bacteria
Pseudomonas aeruginosa 22–44 Ibekwe et al. (1997); Nwabuisi and Ologe (2002); Sharma et al. (2004); Sharma et al. (2010); Dayasena et al. (2011); Afolabi
Downloaded from www.microbiologyresearch.org by

et al. (2012); Kabir et al. (2012); Vishwanath et al. (2012); Asish et al. (2013); Prakash et al. (2013); Orji and Dike (2015)
Staphylococcus aureus 17–37 Dayasena et al. (2011); Vishwanath et al. (2012); Asish et al. (2013); Mariam et al. (2013); Prakash et al. (2013);
Orji and Dike (2015)
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Klebsiella pneumoniae 4–7 Deb and Ray (2012); Vishwanath et al. (2012)
Proteus mirabilis 3–20 Ibekwe et al. (1997); Madana et al. (2011); Deb and Ray (2012); Vishwanath et al. (2012); Orji and Dike (2015)
IP: 114.124.212.22

Proteus vulgaris 0.9–3 Vishwanath et al. (2012)

Escherichia coli 1–21 Deb and Ray (2012); Vishwanath et al. (2012); Orji and Dike (2015)
Streptococcus pneumoniae 1–3 Vishwanath et al. (2012); Prakash et al. (2013)
Acinetobacter baumanii 1–3 Vishwanath et al. (2012); Asish et al. (2013) Prakash et al. (2013)
Enterobacter aerogenes 0.9–4 Vishwanath et al. (2012); Asish et al. (2013)
Anaerobic bacteria
Bacteroides spp. 4–8 Brook (2008); Vishwanath et al. (2012)
Clostridium spp. 3–6 Brook (2008); Vishwanath et al. (2012)
Prevotella spp. 1–3 Brook (2008); Vishwanath et al. (2012)
Fusobacterium nucleatum 3–4 Brook (2008)
Fungi
Aspergillus niger 3–15 Juyal et al. (2014); Vishwanath et al. (2012)
Aspergillus flavus 3–20 Juyal et al. (2014); Vishwanath et al. (2012)
Candida albicans 0.9–23 Juyal et al. (2014); Vishwanath et al. (2012); Asish et al. (2013)
Candida krusei 2–3 Juyal et al. (2014)
Journal of Medical Microbiology 64
R. Mittal and others CSOM: pathogenesis, treatment and hearing loss

Fusobacteriaceae, Pasteurellaceae and Pseudomonadaceae. have been extensively studied in AOM; however, no studies
P. aeruginosa and S. aureus can enter the middle ear are available in relation to CSOM.
through the external canal. P. aeruginosa can thrive well
in the ear environment and is difficult to eradicate. It has
been proposed that P. aeruginosa evades the host defence
mechanism by taking advantage of a shell of surrounding
damaged epithelium that causes decreased blood circula-
tion to the area (Pollack, 1988). P. aeruginosa damages
the tissues, interferes with normal body defences and inac-
tivates antibiotics by various enzymes and toxins (Gellatly
& Hancock, 2013). Bacteroides spp., Clostridium spp.,
Peptococcus spp., Peptostreptococcus spp., Prevetolla melani-
nogenica and Fusobacterium spp. are anaerobic pathogens
that can cause CSOM (Table 2) (Verhoeff et al., 2006;
Prakash et al., 2013). It is possible that some of these
pathogens may be just the normal microbial flora harbour-
ing the middle ear instead of causative agents. However, no
studies are available reporting the normal microflora of the
middle ear. Therefore, further studies are warranted to
characterize the normal microflora of the middle ear,
which will help in differentiating normal ear flora from
the pathogens that cause CSOM.
CSOM can also be characterized by co-infections with more
than one type of bacterial and viral pathogen (Vartiainen &
Vartiainen, 1996; Bakaletz, 2010). Fungi have also been
identified in cultures from patients with CSOM (Ibekwe
et al., 1997; Khanna et al., 2000; Prakash et al., 2013; Asish
et al., 2014; Juyal et al., 2014). However, the presence of
fungi can be due to the treatment with antibiotic ear
drops, which causes suppression of bacterial flora and the
subsequent emergence of fungal flora (Schrader & Isaacson,
2003). This probably increases the incidence of fungal super-
infection, and even the less virulent fungi become more
opportunistic. Furthermore, there has been much disparity
on the rate of isolation of fungi from CSOM patients
(Table 2). This variation can be attributed to the climatic
conditions, as the moist and humid environment favours
the prevalence of fungal infections of the ear.

Pathogenesis
CSOM is considered a multifactorial disease resulting from a
complex series of interactions between environmental,
bacterial, host and genetic risk factors (Rye et al., 2012; Li
et al., 2013). It is important to identify the genes that con-
tribute to CSOM susceptibility, which will provide insights
into the biological complexity of this disease and ultimately
contribute to improve the methods of prevention and
treatment (Allen et al., 2014). Innate host immune mechan-
isms such as the TLR4/MyD88 pathway are particularly
important in eliciting protective immune responses against
bacteria (Hernandez et al., 2008). On the other hand, the
transforming growth factor-b pathway helps in balancing
the adverse outcome of an exaggerated pro-inflammatory
response (Leichtle et al., 2011). The roles of these pathways

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R. Mittal and others CSOM: pathogenesis, treatment and hearing loss

Bacterial biofilms have gained attention in the pathogenesis irreversible tissue changes in the auditory cleft (Kaplan
of CSOM. Biofilms are resistant to antibiotics and other et al., 1996; Sharma et al., 2013). Chronic infection of the
antimicrobial compounds (Stewart & Costerton, 2001;
Hall-Stoodley & Stoodley, 2009; Mah, 2012; Alhede et al.,
2014; Jolivet-Gougeon & Bonnaure-Mallet, 2014; Rö mling
et al., 2014). Therefore, they are difficult to eradicate and
hence could lead to recurrent infections (Donelli &
Vuotto, 2014; Garcı́a-Cobos et al., 2014). In addition, bio-
films attach firmly to damaged tissue, such as exposed ostei-
tic bone and ulcerated middle ear mucosa, or to otological
implants such as tympanostomy tubes, further aggravating
the problem of eradication (Wang et al., 2014). Although
biofilms have been demonstrated in the middle ear of
CSOM patients, their precise role in the pathophysiology
of the disease is yet to be determined (Saunders et al.,
2011; Lampikoski et al., 2012; Kaya et al., 2013; Gu et al.,
2014; Khosravi et al., 2014). Furthermore, the molecular
mechanisms leading to biofilm formation in the middle
ear during CSOM are also poorly understood.
Cytokines have also been implicated in the pathogenesis of
OM. Most of the studies addressing the role of cytokines
are in relation to AOM, and there are very limited studies
available demonstrating the role of cytokines in the patho-
genesis of CSOM. High levels of inflammatory cytokine
such as IL-8 have been demonstrated in the middle ear effu-
sion of CSOM patients (Elmorsy et al., 2010). IL-8 plays a
role in the development of chronicity of OM and has also
been related to bacterial growth. Increased mRNA as well
as protein levels of TNF-a, IL-6, IL-1b and IFN-c have
been found in the middle ear mucosa of CSOM patients
compared with heathy individuals (Si et al., 2014). The upre-
gulation of these pro-inflammatory cytokines can cause
tissue damage as well as transition from acute to chronic
OM. Additional studies are warranted to investigate the
role of cytokines in the pathogenesis of CSOM.

Hearing loss
Hearing impairment is the most common sequela of
CSOM (Aarhus et al., 2015). CSOM can cause conductive
hearing loss (CHL) as well as sensorineural hearing loss
(SNHL). CHL results from the obstruction in the trans-
mission of sound waves from the middle ear to the inner
ear. CSOM is characterized by the presence of fluid
(pus), which can hinder the conductance of sound to the
inner ear. The amount of effusion in the middle ear has
been directly correlated with the magnitude and severity
of CHL (Wiederhold et al., 1980). CSOM is characterized
by the presence of tympanic membrane perforation,
which can hinder the conductance of sound to the inner
ear. The degree to which hearing is compromised has
also been demonstrated to be directly proportional to
the damage caused to the structures of the middle ear
(Yorgancilar et al., 2013b). In some cases of CSOM, there
can be permanent hearing loss that can be attributed to

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Table 3. List of inflammatory mediators generated in the middle ear in response to microbial infection

Inflammatory mediators Possible mode of action References

Nitric oxide Destroys hair cells Huang et al. (1990); Jung et al. (2003)
Reactive oxygen species Morphological changes like cell membrane Clerici et al. (1995)
rupture, blebbing and cell body
shortening

Arachidonic acid metabolites (prostaglandin and Alteration in cochlear blood flow, Jung et al. (1992)
leukotriene) hair cell damage

Histamine Interferes with the efferent innervations Housley et al. (1988)

of the outer hair cells

Cytokines Damage to hair cells Juhn et al. (2008)

Bacterial toxins Block Na/K ATPase and change Guo et al. (1994)
the ion concentration of endolymph;
damage to hair cells

middle ear causes oedema of the middle ear lining and to outer or inner hair cells can cause severe hearing impair-
discharge, tympanic membrane perforation and possibly ment, which can be irreversible and permanent.
ossicular chain disruption, resulting in CHL ranging from
Recent studies have demonstrated that CSOM is able to
20 to 60 dB (Varshney et al., 2010).
cause SNHL in addition to CHL (Papp et al., 2003; da
SNHL results either from inner ear damage (cochlea) or Costa et al., 2009; Kolo et al., 2012; Yang et al., 2014).
injury to the nerve pathways that relay signals from the Infection of the middle ear leads to the generation of
inner ear to the brain. The cochlea in mammals has three inflammatory mediators such as nitric oxide and arachido-
rows of outer hair cells and one row of inner hair cells. nic acid metabolites (Table 3), which can cause functional
The outer hair cells help in the amplification and tuning as well as morphological changes in the auditory structures
of sound waves, whereas inner hair cells are involved in con- (Housley et al., 1988; Jung et al., 1992; Guo et al., 1994;
verting the mechanical energy of sound into an electrical Clerici et al., 1995; Jung et al., 2003). These inflammatory
impulse to be relayed to the auditory nerve. Any damage mediators can also penetrate the round window membrane

Outer ear Middle ear Inner ear

4 OHCs

2 3

IHCs

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Fig. 3. OM and inner ear damage. The bacterial infection of the middle ear (1) leads to the generation of inflammatory
mediators (2) that can penetrate from the round window (3) to the inner ear, leading to damage to outer (OHCs) and inner
(IHCs) auditory hair cells (4).

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R. Mittal and others CSOM: pathogenesis, treatment and hearing loss

and pass into the inner ear causing cochlear damage (Fig. 3) drops. Systemic oral or parenteral antibiotics, although
(Morizono & Tono, 1991; Penha & Escada, 2003; Juhn et al., an option, are less commonly used due to the fact that
2008). The loss of outer and inner hair cells in the basal turn topical antibiotics in combination with aural toilet are
of the cochlea has been observed in CSOM patients (Huang able to achieve significantly higher tissue concentrations
et al., 1990; Cureoglu et al., 2004). The majority of SNHL in than systemic antibiotics (in the order of 100–1000 times
CSOM patients is in the high-frequency range and is unilat- greater). Surgery, in the way of mastoidectomy, was tra-
eral (Jensen et al., 2013). A recent study has also shown that ditionally the mainstay of therapy. However, retrospective
bacterial toxins found in the middle ear during CSOM can studies have suggested that mastoidectomy is not superior
pass into the cochlea and result in cochlear pathology to more conservative therapies such as aural toilet and
(Joglekar et al., 2010). These bacterial toxins can be exotox- topical and systemic antibiotics for uncomplicated CSOM.
ins (proteins) produced by both Gram-positive and Gram-
Reconstruction of the tympanic membrane or tympano-
negative bacteria, or endotoxins (LPSs of the outer mem-
plasty is another surgical technique often used for persistent
brane of Gram-negative bacteria). These infection-associated
toxins might cause direct damage to hair cells, especially perforations after the active infection of CSOM has been
those at the cochlear base where the hair cells are sensitive treated. In addition, surgical eradication of cholesteatoma
to high-frequency sounds (Kolo et al., 2012). A significant is indicated in chronic cholesteatomatous OM (CCOM).
loss of outer and inner hair cells, as well as significant atro-
phy of the stria vascularis in the basal turn of the cochlea,
has been observed in CSOM patients. The basal turn of Aural toilet
the cochlea also demonstrated severe pathological changes The term aural toilet refers to keeping the chronically
that were consistent with the high-frequency SNHL in draining ear clean and dry as much as possible. Techniques
CSOM patients (Cureoglu et al., 2004; Joglekar et al., 2010). include in-office mopping with cotton swabs, suctioning to
SNHL in CSOM patients is often demonstrated by higher remove discharge and debris, and placing an ear wick to
bone conduction (BC) thresholds in the audiogram. BC stent open an oedematous canal (Doshi et al., 2009).
thresholds in the healthy and CSOM ear differed by at least Some practitioners use various powders to help dry the
20 dB at all of the measured frequencies (Luntz et al., ear, many of which include topical antibiotics. One popular
2013). In a multi-centre study, 58 % of 874 patients with uni- example is otic insufflation powder, which consists of a
lateral CSOM presented with SNHL of more than 15 dB in mixture of chloramphenicol, sulfamethoxazol, and ampho-
the affected ear (Paparella et al., 1984). El-Sayed (1998) tericin B (Fungizone). There is no consensus on how often
showed that, in 218 patients, the BC thresholds over a to perform aural toilet or when to use insufflation powder,
range of frequencies were increased by 9.2 to 14.1 dB in but in the case of previous treatment failure, the former can
CSOM ears, with a mean difference between CSOM and be performed daily, if feasible. Some practitioners rec-
normal ears of more than 10 dB in 39 % of patients and of ommend at least two to three times a week, depending
20 dB or more in 12 % of patients. Greater differences at on the severity and duration of symptoms (Dagan et al.,
4000 Hz (5 dB) than at 500, 1000 or 2000 Hz (3 dB) were 1992; Daniel, 2012).
observed in 145 patients with unilateral CSOM (Eisenman
& Parisier, 1998). Significant differences in BC between A small number of randomized controlled studies have
chronic OM and normal ears in 344 patients, ranging from shown that aural toilet is not effective as monotherapy and
0.6 dB at 500 Hz to 3.7 dB at 4000 Hz for all frequencies should be used in combination with medical therapy, ideally
have also been observed (Redaelli de Zinis et al., 2005). da ototopical antibiotics in the treatment of CSOM. Otorrhoea
Costa et al. (2009) reported, in 150 patients, a BC difference resolved frequently in groups treated with a combination of
of 5 dB between chronic OM and normal ears at 1000 and aural toilet, topical and systemic antibiotics, and topical
2000 Hz, increasing to 10 dB at 3000 and 4000 Hz. The per- boric acid compared with aural toilet alone or with no
centage of CSOM patients with higher BC thresholds tended specific therapy (Melaku & Lulseged, 1999; Choi et al.,
to increase with age (Yoshida et al., 2009). The site and size of 2010). Another trial demonstrated that children with
the tympanic membrane perforation have been correlated CSOM treated with aural toilet and intravenous antibiotics
with the degree of hearing loss, with posterior perforations improved more frequently compared with aural toilet
having a greater decibel level loss, probably as a result of alone (Fliss et al., 1990).
loss of protection of the round window membrane from
impinging sound pressure waves (Vaidya et al., 2014).
It was suggested that all measures for an early cure, including Ototopical antibiotics
surgery, should be considered promptly to prevent hearing
loss in CSOM patients (Yoshida et al., 2009). Antibiotic drops in combination with aural toilet are the
mainstay of therapy for CSOM and have been shown to
be the most effective in randomized controlled trials. Qui-
Treatment nolones are the most commonly used topical antibiotics in
The current primary treatment modality for CSOM is a the USA due to their established effectiveness (Aslan et al.,
combination of aural toilet and topical antimicrobial

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1998; Ohyama et al., 1999). Topical quinolones carry a low

side-effect profile and are superior to aminoglycosides
(Nwabuisi & Ologe, 2002). Quinolones are particularly

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effective against P. aeruginosa and do not carry a potential 2006; Daniel, 2012). Topical agents such as quinolones
side effect of cochleotoxicity and vestibulotoxicity, which
are attributed to aminoglycosides (Dohar et al., 1996).
A randomized controlled trial demonstrated that ciproflox-
acin is more effective compared with aminoglycoside, and
another study showed the efficacy of ofloxacin topical anti-
biotic over oral amoxicillin-clavulanic acid in resolving
otorrhoea (Yuen et al., 1994; Couzos et al., 2003).
Corticosteroids are sometimes used in combination with
quinolones for CSOM but are not well studied. Combination
ear drops can be prescribed when there is inflammation of
the external auditory canal or middle ear mucosa, or when
granulation tissue is present. Dexamethasone is often used
in combination with ciprofloxacin for these conditions
(Shinkwin et al., 1996; Hannley et al., 2000; Acuin, 2007).
There are several alternative topical solutions that can be
used in settings in which antibiotic drops are not readily
available. These are used in developed countries but are
much more common in resource-limited settings due to
their low cost and availability. Some of these include acetic
acid, aluminium acetate (Burrow’s solution), or combi-
nations of these (Domeboro’s solution), and iodine-based
antiseptic solutions. Few studies exist comparing these
solutions with ototopical quinolones. However, one retro-
spective study showed that aluminium acetate solution was
as effective as gentamicin in resolving otorrhoea (Clayton
et al., 1990). Also, 57 % of patients in another study had
resolution of otorrhoea after acetic acid irrigations to their
affected ear three times weekly for 3 weeks, in the absence
of any other therapy (Aminifarshidmehr, 1996). Aluminium
acetate can potentially be even more effective than acetic
acid because of its increased activity against many of the
pathogens in vitro (Thorp et al., 1998). Povidone–iodine-
based antiseptic solution has broad-spectrum action against
many organisms that can colonize the middle ear – bacteria,
viruses, fungi and protozoa. One randomized controlled
trial demonstrated that povidone–iodine had the same effi-
cacy as ciprofloxacin drops in resolving otorrhoea (Jaya
et al., 2003). Additionally, it was shown that bacterial resist-
ance rates were much lower for iodine solution than for
ciprofloxacin (Jaya et al., 2003). Further large-scale studies
are warranted to confirm the safety and efficacy of these
topical agents in CSOM.

Systemic antibiotics
Upon failure of primary treatment to resolve otorrhoea
after 3 weeks of therapy, alternative measures must be con-
sidered. Oral antibiotics are a second-line therapy for
CSOM. Systemic therapy has not been as effective as
direct delivery of topical antibiotics due to the inability
to achieve effective concentrations in the infected tissues
of the middle ear. Multiple factors affect drug efficacy
including bioavailability, organism resistance, scarring of
middle ear tissues and decreased vascularization of
middle ear mucosa in chronic disease (Macfadyen et al.,

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are the drug of choice for the second-line therapy (Lang gitis, cerebral abscess and labyrinthine fistula, among
et al., 1992; Kristo & Buljan, 2011). These, however, must others (Kangsanarak et al., 1993; Matin et al., 1997;
be used with caution in children because of the potential
for growth problems related to tendons and joints, and
should be reserved for organisms that are otherwise resist-
ant to other therapies or when there is no safe alternative.
Amoxicillin/clavulanic acid (Augmentin) or erythromycin/
sulfafurazole (Pediazole) are other antibiotics that are
recommended for children.
Intravenous antibiotics have demonstrated efficacy against
CSOM but are not the first-line treatment option for sev-
eral reasons. Due to the risk of systemic side effects and
increased potential to breed antibiotic resistance, intrave-
nous antibiotics should be used as the last-line medical
option for CSOM patients. When possible, antibiotics
should be culture directed, and an infectious disease con-
sultation should be sought, when available. Because the
most common organisms encountered in CSOM are
P. aeruginosa and meticillin-resistant S. aureus (MRSA),
penicillin-based antibiotics and macrolides have very lim-
ited efficacy, as organism resistance rates are high (Brook,
1994; Campos et al., 1995; Park et al., 2008; Choi et al.,
2010). The most effective antibiotics for P. aeruginosa
and MRSA are quinolones, such as ciprofloxacin, and a
combination of vancomycin and trimethoprim-sulfa-
methoxazole (Bactrim), respectively (Park et al., 2008).
Other common antibiotics that can be used against Pseudo-
monas spp. include imipenem and aztreonam (Somekh &
Cordova, 2000). In one study, P. aeruginosa isolates resistant
to ciprofloxacin also demonstrated high resistance to amino-
glycosides, pipercillin-tazobactam, and ceftazidime (Jang &
Park, 2004), making these drugs less-than-ideal candidates
for intravenous therapy. Despite the activity against the
most common infectious agents, intravenous antibiotics
are certainly not a panacea in CSOM. The cure rate of
patients treated with cultured-directed intravenous vanco-
mycin in MRSA CSOM was similar to those treated with
aural toilet and topical acetic acid and aluminium acetate
solutions (Choi et al., 2010). This further demonstrates the
concept that ototopical treatment combined with aggressive
aural toilet is the preferred primary therapeutic modality in
CSOM. Systemic antibiotics should be used for various
degrees of primary treatment failure or when intracranial
complications ensue during CSOM.

Surgery
Surgery should be considered as a last-line resort after
maximal medical therapy has been exhausted for cases of
CSOM that are particularly recalcitrant or recurrent.
Surgery in the form of tympanomastoidectomy is also indi-
cated in cases of CSOM in which there are complications,
some of which could potentially be life threatening, such as
significant hearing loss, facial nerve palsy, subperiosteal
abscess, petrositis, dural venous sinus thrombosis, menin-

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R. Mittal and others CSOM: pathogenesis, treatment and hearing loss

Taylor & Berkowitz, 2004; Matanda et al., 2005; Zanetti & CSOM are still poorly understood. There is an urgent
Nassif, 2006; Dubey & Larawin, 2007; Akinpelu et al., 2008; need to focus research studies in the area of CSOM,
Mostafa et al., 2009). Chronic cholesteatomatous OM which will open up avenues to design novel therapeutic
requires surgery, usually in the form of tympanomastoi- studies against CSOM and hence prevent hearing loss.
dectomy in order to eradicate cholesteatoma, a usual Medical and surgical options are limited, with side effects
underlying cause of chronic infection (Shirazi et al., 2006). and risks, and sometimes are not successful in eliminating
However, some retrospective studies show that there is no disease. Topical antibiotics, which are the first-line therapy
difference in outcomes of graft success rate or post-operative of choice, are limited only to those that are not potentially
hearing with regard to whether mastoidectomy is performed ototoxic. Additionally, surgery carries the risks of worsen-
in addition to tympanoplasty (Balyan et al., 1997; Mishiro ing hearing, as well as the potential for damage to the facial
et al., 2001). Mastoidectomy may be indicated to reduce nerve and resulting facial nerve paresis.
the burden of disease in cases with abscess formation in
It is likely that some of the factors involved in AOM may
the mastoid, tympanoplasty or recalcitrant disease (Collins
also be involved in CSOM; however, it is also possible
et al., 2003; Angeli et al., 2006).
that there are significant differences that need to be eluci-
Tympanoplasty can be performed anywhere from 6 to dated in further studies. There is a need to characterize
12 months after resolution of the infection. A large percentage the role of immunity (both innate and adaptive) as it per-
of perforations will heal on their own after resolution of infec- tains to the transition from AOM to CSOM. Establishing
tion, but in those that do not, tympanoplasty is indicated to animal models of CSOM will help in elucidating the role
improve hearing and to help prevent recurrence of infection of microbial biofilms and virulence factors, as well as
by closing off the middle ear space. In addition, patients host factors in the CSOM pathogenesis. These models
must practice dry ear precautions to help decrease the rate of will also help in evaluating the potency and efficacy of
recurrent infection and otorrhoea (Bluestone, 1988). novel treatment strategies against CSOM. Recently, a
mouse model of CSOM has been reported (Santa Maria
et al., 2015) that can be explored to understand host–
Recurrent disease
pathogen interactions during CSOM and the development
Recurrent CSOM (patients who develop CSOM, recover of novel treatment modalities against the disease. Emerging
from disease and develop chronic infection again) is due new technologies such as systems biology approaches
to one or a combination of several factors. These include employing high-throughput multiomics techniques (geno-
treatment with oral antibiotics alone, treatment with non- mics, transcriptomics, proteomics and metabolomics) can
antibiotic drops, non-compliance with the treatment regi- be used to construct predictive models of the networks
men, infection with resistant bacteria such as P. aeruginosa and dynamic interactions between the biological com-
or MRSA, and the presence of cholesteatoma. Disease can ponents of the complex host–pathogen system. Advances
also be particularly recalcitrant and recurrent in patients in sequencing technology have revolutionized pathogen
with a distorted ear anatomy or who are prone to infections. biology and opened up unprecedented opportunities to
Recurrent disease can be managed by ototopical antibiotic understand the pathologies of intractable infectious dis-
therapy during the active infection and by several additional eases. Development of computational methods to probe
methods to prevent relapse. The most conservative of these these ‘ultra-fast’ ‘omics’ data to discover new pathogens
measures are dry ear precautions and aural toilet (Bluestone, or deconstruct the molecular network underlying host–
1988). Prophylactic antibiotics have been used but are not pathogen interactions is increasingly being pursued, and
recommended to prevent recurrent disease, as this may lead is likely to catalyse the development of new clinical
to antibiotic resistance and difficulty with treatment in the approaches for tackling CSOM. Bacteriophages can be a
future (Arguedas et al., 1994). Upon resolution of the active viable option for the treatment of bacterial infections due
infection, tympanoplasty may be performed to help prevent to the emergence of multidrug-resistant strains (Samson
chronic drainage by sealing off the middle ear, assisting in et al., 2013; Viertel et al., 2014; Qadir, 2015). Bacterio-
proper Eustachian tube function, and preventing microbial phages are viruses that specifically and uniquely destroy
entry into the middle ear space (Rickers et al., 2006; Shim bacteria. Bacteriophages are considered safe, economical,
et al., 2010). When a child develops recurrent disease, com- self-replicating and effective bactericidal agents (Golkar
puted tomographic imaging of the temporal bones should et al., 2014; Jassim and Limoges, 2014). In a small con-
be sought to evaluate for potential cholesteatoma or mastoid
trolled clinical trial with 24 patients, bacteriophages
abscess formation, as these are surgically correctable causes of
provided efficient protection and demonstrated efficacy
recurrent or persistent CSOM.
against chronic otitis media caused by chemoresistant
P. aeruginosa (Wright et al., 2009). Further large-scale ran-
Conclusions domized double-blind clinical trials are warranted to
explore the translational potential of bacteriophages against
CSOM is the most common chronic infectious disease CSOM. In addition, studies are warranted to characterize
worldwide. The factors underlying the pathogenesis of

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R. Mittal and others CSOM: pathogenesis, treatment and hearing loss

middle ear and inner ear interactions during CSOM

pathogenesis. This is especially true regarding the role of

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R. Mittal and others CSOM: pathogenesis, treatment and hearing loss

inflammatory mediators that appear to be capable of cross- Arguedas, A., Loaiza, C., Herrera, J. F. & Mohs, E. (1994).
ing the round window membrane and causing potentially Antimicrobial therapy for children with chronic suppurative otitis
permanent hearing loss via damage to auditory hair cells. media without cholesteatoma. Pediatr Infect Dis J 13, 878–882.
The identification of genetic and prognostic markers will Asish, J., Amar, M., Vinay, H., Sreekantha, Avinash, S. S. &
help in predicting CSOM-susceptible individuals and poss- Amareshar, M. (2013). To study the bacteriological and mycological
ibly even novel therapeutic strategies. Understanding the profile of chronic suppurative otitis media patients and their
antibiotic sensitivity pattern. Int J Pharma Bio Sci 4, 186–199.
molecular mechanisms leading to CSOM will provide
avenues to design novel treatment modalities against the Aslan, A., Altuntas, A., Titiz, A., Arda, H. N. & Nalca, Y. (1998). A new
disease and consequent hearing loss. dosage regimen for topical application of ciprofloxacin in the
management of chronic suppurative otitis media. Otolaryngol Head
Neck Surg 118, 883–885.
Bakaletz, L. O. (2010). Immunopathogenesis of polymicrobial otitis
media. J Leukoc Biol 87, 213–222.
ACKNOWLE DGEMENTS
Balyan, F. R., Celikkanat, S., Aslan, A., Taibah, A., Russo, A. & Sanna,
The research work in Dr Liu’s laboratory is supported by the National M. (1997). Mastoidectomy in noncholesteatomatous chronic
Institutes of Health/National Institute on Deafness and Other Com- suppurative otitis media: is it necessary? Otolaryngol Head Neck
munication Disorders grants R01 DC05575, R01 DC01246 and R01 Surg 117, 592–595.
DC012115. We are thankful to April Mann for the critical reading Bluestone, C. D. (1988). Current management of chronic suppurative
of the manuscript. otitis media in infants and children. Pediatr Infect Dis J 7 (Suppl.),
S137–S140.
Bluestone, C. D. (1998). Epidemiology and pathogenesis of chronic
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