Introduction

A nosocomial infection — also called “hospital-

acquired infection” can be defined as:
Eastern Mediterranean and South-East Asia Regions
(11.8 and 10.0% respectively), with a prevalence of
7.7 and 9.0% respectively in the European and West-
An infection acquired in hospital by a patient who was
ern Pacific Regions (4).
admitted for a reason other than that infection (1). An in-
fection occurring in a patient in a hospital or other health The most frequent nosocomial infections are infec-
care facility in whom the infection was not present or incu- tions of surgical wounds, urinary tract infections and
bating at the time of admission. This includes infections lower respiratory tract infections. The WHO study,
acquired in the hospital but appearing after discharge, and and others, have also shown that the highest preva-
also occupational infections among staff of the facility (2). lence of nosocomial infections occurs in intensive
care units and in acute surgical and orthopaedic
Patient care is provided in facilities which range from
wards. Infection rates are higher among patients with
highly equipped clinics and technologically ad-
increased susceptibility because of old age, under-
vanced university hospitals to front-line units with
lying disease, or chemotherapy.
only basic facilities. Despite progress in public health
and hospital care, infections continue to develop in
hospitalized patients, and may also affect hospital
Impact of nosocomial infections
staff. Many factors promote infection among hospi-
talized patients: decreased immunity among patients; Hospital-acquired infections add to functional dis-
the increasing variety of medical procedures and ability and emotional stress of the patient and may,
invasive techniques creating potential routes of in some cases, lead to disabling conditions that re-
infection; and the transmission of drug-resistant duce the quality of life. Nosocomial infections are
bacteria among crowded hospital populations, where also one of the leading causes of death (5). The eco-
poor infection control practices may facilitate trans- nomic costs are considerable (6,7). The increased
mission. length of stay for infected patients is the greatest
contributor to cost (8,9,10). One study (11) showed
that the overall increase in the duration of hospi-
Frequency of infection talization for patients with surgical wound infections
was 8.2 days, ranging from 3 days for gynaecology
Nosocomial infections occur worldwide and affect
to 9.9 for general surgery and 19.8 for orthopaedic
both developed and resource-poor countries. Infec-
surgery. Prolonged stay not only increases direct costs
tions acquired in health care settings are among the
to patients or payers but also indirect costs due to
major causes of death and increased morbidity
lost work. The increased use of drugs, the need for
among hospitalized patients. They are a significant
isolation, and the use of additional laboratory and
burden both for the patient and for public health. A
other diagnostic studies also contribute to costs.
prevalence survey conducted under the auspices of
Hospital-acquired infections add to the imbalance
WHO in 55 hospitals of 14 countries representing
between resource allocation for primary and sec-
4 WHO Regions (Europe, Eastern Mediterranean,
ondary health care by diverting scarce funds to the
South-East Asia and Western Pacific) showed an
management of potentially preventable conditions.
average of 8.7% of hospital patients had nosocomial
infections. At any time, over 1.4 million people world- The advancing age of patients admitted to health
wide suffer from infectious complications acquired care settings, the greater prevalence of chronic dis-
in hospital (3). The highest frequencies of nosoco- eases among admitted patients, and the increased
mial infections were reported from hospitals in the use of diagnostic and therapeutic procedures which

1
 PREVENTION OF HOSPITAL-ACQUIRED INFECTIONS: A PRACTICAL GUIDE — WHO/CDS/CSR/EPH/2002.12

affect the host defences will provide continuing disease, and diagnostic and therapeutic interventions.
pressure on nosocomial infections in the future. The extremes of life — infancy and old age — are as-
Organisms causing nosocomial infections can be sociated with a decreased resistance to infection.
transmitted to the community through discharged Patients with chronic disease such as malignant tu-
patients, staff, and visitors. If organisms are multire- mours, leukaemia, diabetes mellitus, renal failure,
sistant, they may cause significant disease in the or the acquired immunodeficiency syndrome (AIDS)
community. have an increased susceptibility to infections with
opportunistic pathogens. The latter are infections
with organism(s) that are normally innocuous, e.g.
Factors influencing the development of part of the normal bacterial flora in the human, but
nosocomial infections may become pathogenic when the body’s immuno-
The microbial agent logical defences are compromised. Immunosuppres-
sive drugs or irradiation may lower resistance to
The patient is exposed to a variety of microorgan- infection. Injuries to skin or mucous membranes
isms during hospitalization. Contact between the bypass natural defence mechanisms. Malnutrition is
patient and a microorganism does not by itself nec- also a risk. Many modern diagnostic and therapeu-
essarily result in the development of clinical disease tic procedures, such as biopsies, endoscopic exami-
— other factors influence the nature and frequency nations, catheterization, intubation/ventilation and
of nosocomial infections. The likelihood of expo- suction and surgical procedures increase the risk of
sure leading to infection depends partly on the char- infection. Contaminated objects or substances may
acteristics of the microorganisms, including resistance be introduced directly into tissues or normally ster-
to antimicrobial agents, intrinsic virulence, and ile sites such as the urinary tract and the lower res-
amount (inoculum) of infective material. piratory tract.
Many different bacteria, viruses, fungi and parasites
may cause nosocomial infections. Infections may be
caused by a microorganism acquired from another Environmental factors
person in the hospital (cross-infection) or may be Health care settings are an environment where both
caused by the patient’s own flora (endogenous in- infected persons and persons at increased risk of
fection). Some organisms may be acquired from an infection congregate. Patients with infections or car-
inanimate object or substances recently contami- riers of pathogenic microorganisms admitted to
nated from another human source (environmental hospital are potential sources of infection for pa-
infection). tients and staff. Patients who become infected in the
Before the introduction of basic hygienic practices hospital are a further source of infection. Crowded
and antibiotics into medical practice, most hospital conditions within the hospital, frequent transfers of
infections were due to pathogens of external origin patients from one unit to another, and concentra-
(foodborne and airborne diseases, gas gangrene, teta- tion of patients highly susceptible to infection in one
nus, etc.) or were caused by microorganisms not area (e.g. newborn infants, burn patients, intensive
present in the normal flora of the patients (e.g. diph- care ) all contribute to the development of nosoco-
theria, tuberculosis). Progress in the antibiotic treat- mial infections. Microbial flora may contaminate
ment of bacterial infections has considerably reduced objects, devices, and materials which subsequently
mortality from many infectious diseases. Most in- contact susceptible body sites of patients. In addi-
fections acquired in hospital today are caused by tion, new infections associated with bacteria such as
microorganisms which are common in the general waterborne bacteria (atypical mycobacteria) and/or
population, in whom they cause no or milder dis- viruses and parasites continue to be identified.
ease than among hospital patients (Staphylococcus
aureus, coagulase-negative staphylococci, enterococci,
Enterobacteriaceae). Bacterial resistance
Many patients receive antimicrobial drugs. Through
selection and exchange of genetic resistance elements,
Patient susceptibility
antibiotics promote the emergence of multidrug-
Important patient factors influencing acquisition of resistant strains of bacteria; microorganisms in the
infection include age, immune status, underlying normal human flora sensitive to the given drug are

2
 INTRODUCTION

suppressed, while resistant strains persist and may References

become endemic in the hospital. The widespread use
1. Ducel G et al. Guide pratique pour la lutte contre
of antimicrobials for therapy or prophylaxis (includ-
l’infection hospitalière. WHO/BAC/79.1.
ing topical) is the major determinant of resistance.
Antimicrobial agents are, in some cases, becoming 2. Benenson AS. Control of communicable diseases
less effective because of resistance. As an antimicro- manual, 16th edition. Washington, American Pub-
bial agent becomes widely used, bacteria resistant lic Health Association, 1995.
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the health care setting. Many strains of pneumo- of Hospital Infections. Chemiotherapia, 1987, 3:148–
cocci, staphylococci, enterococci, and tuberculosis are 151.
currently resistant to most or all antimicrobials which
were once effective. Multiresistant Klebsiella and Pseu- 4. Mayon-White RT et al. An international survey
domonas aeruginosa are prevalent in many hospitals. of the prevalence of hospital-acquired infection.
This problem is particularly critical in developing J Hosp Infect, 1988, 11 (Supplement A):43–48.
countries where more expensive second-line anti- 5. Ponce-de-Leon S. The needs of developing coun-
biotics may not be available or affordable (12). tries and the resources required. J Hosp Infect, 1991,
18 (Supplement):376–381.

Nosocomial infections are widespread. They are im- 6. Plowman R et al. The socio-economic burden of hospi-
portant contributors to morbidity and mortality.They tal-acquired infection. London, Public Health Labo-
will become even more important as a public health ratory Service and the London School of Hygiene
problem with increasing economic and human impact and Tropical Medicine, 1999.
because of: 7. Wenzel RP. The economics of nosocomial infec-
● Increasing numbers and crowding of people. tions. J Hosp Infect 1995, 31:79–87.

● More frequent impaired immunity (age, illness, 8. Pittet D, Taraara D, Wenzel RP. Nosocomial blood-
treatments). stream infections in critically ill patients. Excess
length of stay, extra costs, and attributable mor-
● New microorganisms. tality. JAMA, 1994, 271:1598–1601.
● Increasing bacterial resistance to antibiotics (13). 9. Kirkland KB et al. The impact of surgical-site in-
fections in the 1990’s: attributable mortality, ex-
cess length of hospitalization and extra costs. Infect
Purpose of this manual Contr Hosp Epidemiol, 1999, 20:725–730.

This manual has been developed to be a practical, 10. Wakefield DS et al. Cost of nosocomial infection:
basic, resource which may be used by individuals relative contributions of laboratory, antibiotic,
with an interest in nosocomial infections and their and per diem cost in serious Staphylococcus aureus
control, as well as those who work in nosocomial infections. Amer J Infect Control, 1988, 16:185–192.
infection control in health care facilities. It is appli-
11. Coella R et al. The cost of infection in surgical
cable to all facilities, but attempts to provide rational
patients: a case study. J Hosp Infect, 1993, 25:239–
and attainable recommendations for facilities with
250.
relatively limited resources. The information should
assist administrators, infection control personnel, and 12. Resources. In: Proceedings of the 3rd Decennial Inter-
patient care workers in such facilities in the initial national Conference on Nosocomial Infections, Preventing
development of a nosocomial infection control pro- Nosocomial Infections. Progress in the 80’s. Plans for the
gramme, including specific components of such pro- 90’s, Atlanta, Georgia, July 31–August 3, 1990:30
grammes. Additional reading in specific areas is (abstract 63).
provided in the list of WHO relevant documents and 13. Ducel G. Les nouveaux risques infectieux.
infection control texts at the end of the manual (An- Futuribles, 1995, 203:5–32.
nex 1), as well as relevant references in each chapter.