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Covid-19 (Pandemic): A Review Article

Alisha Ishrath1*, Mohammed Mazher Ahmed2, Namarata Pal3, Siri Muppidi4

1Department of Pharmaceutical Biotechnology, Mesco College of Pharmacy, Hyderabad, India

2Department of Pharmaceutics, Luqman College of Pharmacy, Gulbarga, Karnataka, India

3Department of Microbiology, Shoolini University, Himachal Pradesh, India

4Department of Pharmacology, Gokuraju Gangaraju College of Pharmacy, Hyderabad, India

ABSTRACT
Coronaviruses are a group of enveloped viruses with nonsegmented, single-stranded, and positive-sense RNA genomes.
Coronaviruses belong to the “Coronaviridae family”, which causes various diseases, from the common cold to SARS and
MERS. In March 2020 the World Health Organization declared the SARS-Cov-2 virus a global pandemic. We performed a
review to describe existing literature about Corona Virus Disease 2019 (COVID-19) history, Symptoms, Epidemiology,
Clinical features, Clinical manifestations, Diagnosis, Treatment, Prevention.

Key words: COVID-19, Symptoms, Epidemiology, Clinical features, Clinical manifestations, Diagnosis, Treatment,
Prevention

HOW TO CITE THIS ARTICLE: Alisha Ishrath, Mohammed Mazher Ahmed, Namarata Pal, Siri Muppidi, Covid-19 (Pandemic): A Review Article, J Res Med
Dent Sci, 2021, 9(10): 281-288.

Corresponding author: Alisha Ishrath Transcription Polymerase Chain Reaction (RT-qPCR) or by

e-mail✉: alisha.ishrath95@gmail.com
Rapid Antigen Test (RAT) [3].
Received: 26/09/2021
Accepted: 12/10/2021 Coronavirus (CoV) is clustered under the viral family
group that causes disease in mammals and birds. A
INTRODUCTION pandemic novel coronavirus was named as ‘‘Corona Virus
Disease 2019’’ (2019-nCoV) by World Health Organization
The human body is exposed to a variety of infectious
(WHO) in Geneva, Switzerland. As its RNA pattern is closer
microorganisms, such as viruses, bacteria, fungi, protozoa,
to SARS, the 2019 Coronavirus is renamed as SARSCoV- 2
and helminths, which cause tissue damage through
pandemic. It belongs to the subfamily Orthocoronavirinae
different mechanisms. Viruses are unique among these
inside the family Coronaviridae, order Nidovirales, and the
five types of infectious organisms in that they can
realm Riboviria [4]. A two-dimensional view of Corona
manipulate the host-cell machinery in a unique way and
beneath a transmission electron microscopy reveals a
continuously evolve to survive and prosper in all species
characteristic look of ‘‘paying homage to a crown’’ around
[1].
the virions. This lead to naming the virus ‘‘Corona’’,
COVID-19 is the disease caused by a new coronavirus meaning ‘‘crown’’ or ‘‘halo’’ in Latin
called SARS-CoV-2. WHO first learned of this new virus on
This is the deadly third-generation virus in Corona family
31 December 2019, following a report of a cluster of cases
preceded by severe acute respiratory syndrome (SARS) in
of ‘viral pneumonia’ in Wuhan, People’s Republic of China
2003, killed almost 10% of total affected patients (8429)
[2].
across 29 international locations and Middle East
Since December 2019, a novel coronavirus disease had Respiratory Syndrome (MERS) in 2012, even more lethal
rapidly spread throughout China, leading to a global with a mortality rate of 30% of the infected patients [4].
outbreak, and causing considerable public health concern.
World Health Organisation (WHO) announced the HISTORY
outbreak of COVID-19 as a global public health emergency
Coronaviruses are enveloped positive sense RNA viruses
on 30 January 2020. In India, the first case of COVID-19
ranging from 60 nm to 140 nm in diameter with spike like
was reported on January 27, 2020, in Kerala district. Since
projections on its surface giving it a crown like appearance
then, there is a wide variation in the reporting of cases
under the electron microscope; hence the name
across the country. The case reporting is based on the
coronavirus [3]. Four corona viruses namely HKU1, NL63,
SARS-CoV-2 antigen testing by Real-Time Reverse

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Fathima Hinaz Z, et al. J Res Med Dent Sci, 2021, 9 (10): 281-288

229E and OC43 have been in circulation in humans, and • Loss of appetite.
generally cause mild respiratory disease. • Confusion.
There have been two events in the past two decades • Persistent pain or pressure in the chest.
wherein crossover of animal betacorona viruses to • High temperature (above 38 °C).
humans has resulted in severe disease. The first such Other less common symptoms are
instance was in 2002–2003 when a new coronavirus of
the β genera and with origin in bats crossed over to • Irritability.
humans via the intermediary host of palm civet cats in • Confusion.
the Guangdong province of China. This virus, designated • Reduced consciousness (sometimes associated with
as severe acute respiratory syndrome coronavirus seizures).
affected 8422 people mostly in China and Hong Kong and • Anxiety.
caused 916 deaths (mortality rate 11%) before being
• Depression.
contained. Almost a decade later in 2012, the Middle East
• Sleep disorders.
respiratory syndrome coronavirus (MERS-CoV), also of
bat origin, emerged in Saudi Arabia with dromedary • More severe and rare neurological complications such
camels as the intermediate host and affected 2494 people as strokes, brain inflammation, delirium and nerve
and caused 858 deaths (fatality rate 34%) [5]. damage.
People of all ages who experience fever and/or cough
SYMPTOMS associated with difficulty breathing or shortness of
A wide range of symptoms are found in COVID-19 breath, chest pain or pressure, or loss of speech or
patients, ranging from mild/moderate to severe, rapidly movement should seek medical care immediately. If
progressive, and fulminant disease. Symptoms of possible, call your health care provider, hotline or health
COVID-19 are non-specific and disease presentation can facility first, so you can be directed to the right clinic [1].
range from asymptomatic to severe pneumonia.
Incidence of asymptomatic cases ranges from 1.6% to EPIDEMIOLOGY
51.7% and these people do not present typical clinical All ages are at risk of getting the illness. This is because
symptoms or signs and do not present apparent the ailment is transmitted through large droplets that
abnormalities in lung computed tomography. The most result from coughing and sneezing by symptomatic
common symptoms of COVID-19 are fever, cough, individuals. In some instances, the infection can happen
myalgia, or fatigue and atypical symptoms include from asymptomatic individuals and before the beginning
sputum, headache, haemoptysis, vomiting, and diarrhoea. of symptoms. As of March 2020, the WHO announced
Some patients may present with sore throat, rhinorrhoea, that there are about 87,317 cases of COVID- 19 globally
headache, and confusion a few days before the onset of as well as confirmed cases of deaths is 2,977. This implies
fever, indicating that fever is a critical symptom, but not that the disease symptoms are mild as only 3.42 per cent
the initial manifestation of infection. Furthermore, some of patients with it have died because of the virus. At the
patients experience loss of smell (hyposmia) or taste same time, the high number of incidences and deaths
(hypogeusia), which are now being considered early have been identified in China. It is that 92 per cent of the
warning signs and indications for self-isolation [6]. total number of occurrences have been reported in Asia,
The most common symptoms of COVID-19 are mainly China. Importantly, the confirmed incidences are
clinically identified and laboratory-confirmed. Further,
• Fever. outside Asia, the number of cases and deaths differs due
• Dry cough. to the on-going nature of the disease, population density,
• Fatigue. degree of testing and reporting, and timing of reducing
strategies. The features of COVID-19 are categorized into
Other symptoms that are less common and may affect
the host of the virus, transmission mode and incubation
some patients include
period. In the first place, the Chinese horseshoe bat is the
• Loss of taste or smell. natural hosts and the terminal hosts are humans. Also,
• Nasal congestion. the transmission is from individual to individual through
• Conjunctivitis (also known as red eyes). aerosol droplets. Lastly, the incubation period varies
from two to fourteen days. Therefore, COVID-19
• Sore throat.
cumulative incidence differs depending on the country
• Headache. and incidences have been confirmed in almost all
• Muscle or joint pain. continents [7].
• Different types of skin rash.
• Nausea or vomiting. GEOGRAPHIC DISTRIBUTION
• Diarrhea.
Since the initial report from China, the disease spread
• Chills or dizziness. rapidly, and the number of cases increased exponentially.
Symptoms of severe COVID-19 disease include: On January 11, the first case was reported outside
mainland China in Thailand,7 and within months, the
• Shortness of breath. disease spread to all the continents except Antarctica.
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India reported its first case of COVID-19 on January 30, critical. The shared symptoms of individuals with the
2020. This rose to three cases by February 3, 2020. No disease include fever (98.6 per cent), tiredness (69.6 per
further cases were reported in February 2020. However, cent), dry cough, and looseness of the bowels.
by mid-March, the number of infected cases started to
increase, and many cases were reported from all over Asymptomatic infections
India. The first COVID-19 related death in India was
Asymptomatic infections have been well documented
reported on March 12, 2020. By the second week of April,
[19-27]. One review estimated that 33 percent of people
the disease spread to all states in India except Sikkim. At
with SARS-CoV-2 infection never develop symptoms [28].
the time of writing this manuscript, there have been
This estimate was based on four large population-based,
2,170,265 cases and 135,163 deaths globally and 15,712
cross-sectional surveys, among which the median
cases and 507 deaths in India [8,9].
proportion of individuals who had no symptoms at the
time of a positive test was 46 percent (range 43 to 77
TRANSMISSION
percent), and on 14 longitudinal studies, among which a
Zoonotic transmission initially appeared to be a plausible median of 73 percent of initially asymptomatic
cause as majority of early cases had a history of exposure individuals remained so on follow-up. However, there is
to wet markets [10]. However, by the end of January still uncertainty around the proportion of asymptomatic
2020, the number of people who developed the disease infections, with a wide range reported across studies.
without exposure to the market or another person with Additionally, the definition of "asymptomatic" may vary
respiratory symptoms increased. The spread of the across studies, depending on which specific symptoms
disease among persons who did not visit Wuhan and were assessed. The range of findings in studies
among healthcare workers suggested a person-to-person evaluating asymptomatic infections is reflected in the
spread of the virus [11,12]. The exact mode of following examples:
transmission of this virus is unknown. But, as with other
• In a COVID-19 outbreak on a cruise ship where nearly
respiratory viruses, droplet borne infection, either
all passengers and staff were screened for severe
directly or indirectly, through fomites is probably the
acute respiratory syndrome coronavirus 2 (SARS-
predominant mode of transmission. At present, there is
CoV-2), approximately 19 percent of the population
no evidence for airborne transmission of the virus.12 13
on board tested positive; 58 percent of the 712
Although virus particles have been detected in stool
confirmed COVID-19 cases were asymptomatic at the
samples of both symptomatic and convalescing patients,
time of diagnosis [29,30]. In studies of subsets of
the risk of feco-oral transmission is unclear [13].
those asymptomatic individuals, who were
hospitalized and monitored, approximately 77 to 89
Period of Infectivity
percent remained asymptomatic over time [30,31].
The duration for which a patient with COVID-19 remains • In a smaller COVID-19 outbreak within a skilled
infective is unclear. Viral load in the oropharyngeal nursing facility, 27 of the 48 residents (56 percent)
secretions is highest during the early symptomatic stage who had a positive screening test were asymptomatic
of the disease [13,14]. The patient can continue to shed at the time of diagnosis, but 24 of them developed
the virus even after symptom resolution [13]. In a study symptoms over the next seven days [32].
from China, the median duration of virus shedding was • Other studies, particularly those conducted among
20 days (interquartile range [IQR] 17.0–24.0) amongst younger populations, have reported even higher
the survivors [15]. A study of viral dynamics in mild and proportions of infections that are asymptomatic
severe cases revealed that mild cases tend to clear the [33-37]. As an example, in an outbreak on an aircraft
viruses early, while severe cases can have prolonged viral carrier, a quarter of the crew, among whom the mean
shedding [16]. Data from studies using twin respiratory age was 27 years, tested positive for SARS-CoV-2 [36].
and fecal sampling have shown viral shedding can persist Among the 1271 cases, only 22 percent were
in stools for more than 4 weeks even when respiratory symptomatic at the time of testing and 43 percent
samples are negative [17]. Xu et al identified male sex, remained asymptomatic throughout the observation
delayed hospitalization after illness, and invasive period. High rates of asymptomatic infection have
mechanical ventilation as risk factors for prolonged viral also been reported among pregnant women
shedding [13]. Transmission during the asymptomatic presenting for delivery [2,34].
phase has also been reported. In a study from Singapore,
6.4% of the 157 locally acquired cases of COVID-19 were Patients with asymptomatic infection may have objective
attributed to transmission during the asymptomatic clinical abnormalities [24,38]. As an example, in a study
phase of the disease [18]. of 24 patients with asymptomatic infection who all
underwent chest computed tomography (CT), 50 percent
CLINICAL FEATURES had typical ground-glass opacities or patchy shadowing,
and another 20 percent had atypical imaging
The clinical features of this ailment vary, extending from abnormalities [38]. Five patients developed low-grade
an asymptomatic state to acute respiratory distress fever, with or without other typical symptoms, a few days
syndrome to septic shock and multi-organ dysfunction. after diagnosis. In another study of 55 patients with
Ideally, this ailment is categorized depending on its asymptomatic infection identified through contact
severity and this include mild, moderate, severe, and tracing, 67 percent had CT evidence of pneumonia on
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Fathima Hinaz Z, et al. J Res Med Dent Sci, 2021, 9 (10): 281-288

admission; only two patients developed hypoxia, and all analysis of hospital data from the United States Veterans
recovered [24]. Health Administration, patients with COVID-19 were five
times more likely to die during the hospitalization than
As above, some individuals who are asymptomatic at the
patients with influenza (21 versus 3.8 percent) [44].
time of diagnosis go on to develop symptoms (ie, they
were actually presymptomatic). In one study, symptom Over the course of the pandemic, declining in-hospital
onset occurred a median of four days (range of three to fatality rates have been reported [61-64]. As an example,
seven) after the initial positive RT-PCR test [30]. in a retrospective study of a national surveillance
database in England that included over 21,000 critical
SEVERITY OF SYMPTOMATIC INFECTION care patients with COVID-19, ICU survival improved from
58 percent in late March 2020 to 80 percent by June
Spectrum of infection severity 2020 [61]. The reasons for this observation are
uncertain, but potential explanations include
The spectrum of symptomatic infection ranges from mild improvements in hospital care of COVID-19 and better
to critical; most infections are not severe [19,39-44]. allocation of resources when hospitals were not
Specifically, in a report from the Chinese Centre for overburdened.
Disease Control and Prevention that included
approximately 44,500 confirmed infections with an In resource-limited settings, in-hospital mortality rates
estimation of disease severity [45]: may be higher than those reported elsewhere. As an
example, in a study from 10 countries in Africa, where
• Mild disease (no or mild pneumonia) was reported in there was a median of two intensive care specialists in
81 percent. each hospital and a minority of facilities did not have
• Severe disease (eg, with dyspnea, hypoxia, or >50 pulse oximetry, the in-hospital 30-day mortality rate
percent lung involvement on imaging within 24 to 48 following critical care admission was 48 percent [65].
hours) was reported in 14 percent. Mortality was associated with underlying comorbidities
• Critical disease (eg, with respiratory failure, shock, or as well as resource shortages.
multiorgan dysfunction) was reported in 5 percent.
• The overall case fatality rate was 2.3 percent; no Excess deaths during the pandemic
deaths were reported among noncritical cases.
Neither the case fatality rate nor the infection fatality rate
Similarly, in a report of 1.3 million cases reported to the account for the full burden of the pandemic, which
United States Centers for Disease Control and Prevention includes excess mortality from other conditions because
(CDC) through the end of May 2020, 14 percent were of delayed care, overburdened health care systems, and
hospitalized, 2 percent were admitted to the intensive social determinants of health [66-68].
care unit (ICU), and 5 percent died [46]. The risk of
severe illness varied by age and underlying Incubation period and serial interval
comorbidities.
The mean or median incubation period of the disease
ranges from 5 to 6 days [69,70]. Lauer et al estimated
Infection fatality rates
that 2.5% of the patients will develop symptoms within
The case fatality rate only indicates the mortality rate 2.2 days (95% CI, 1.8 to 2.9 days) and 97.5% of patients
among documented cases. Since many severe acute will develop symptoms within 11.5 days (95% CI, 8.2–
respiratory syndrome coronavirus 2 (SARS-CoV-2) 15.6 days).
infections are asymptomatic and many mild infections do
Serial interval refers to the time interval between the
not get diagnosed, the infection fatality rate (i.e., the
onset of symptoms in the primary case and the
estimated mortality rate among all individuals with
secondary case. The mean serial interval is estimated to
infection) is considerably lower and has been estimated
be approximately 4 to 5 days [71,72]. By analysing data
in some analyses to be between 0.15 and 1 percent, with
from 468 infector–infectee pairs, Du et al noted that 59
substantial heterogeneity by location and across risk
secondary cases had symptoms earlier than their
groups [47-50].
primary case. This suggested that there is a possibility
that the transmission of the disease occurred during the
Fatality rates among hospitalized patients
asymptomatic phase of illness in this group of patients
Among hospitalized patients, the risk of critical or fatal [73].
disease is high [51-57]. In a study from early in the
pandemic that included 2741 patients who were Period of Infectivity
hospitalized for COVID-19 in a New York City health care
The duration for which a patient with COVID-19 remains
system, 665 patients (24 percent) died or were
infective is unclear. Viral load in the oropharyngeal
discharged to hospice [54]. Of the 647 patients who
secretions is highest during the early symptomatic stage
received invasive mechanical ventilation, 60 percent died,
of the disease [74]. The patient can continue to shed the
13 percent were still ventilated, and 16 percent were
virus even after symptom resolution. In a study from
discharged by the end of the study. The in-hospital
China, the median duration of virus shedding was 20
fatality rate associated with COVID-19 has been higher
days (interquartile range [IQR] 17.0–24.0) amongst the
than that for influenza [58-60]. As an example, in an

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Fathima Hinaz Z, et al. J Res Med Dent Sci, 2021, 9 (10): 281-288

survivors [75]. A study of viral dynamics in mild and or PCR testing. The antigen test is often used as a point-
severe cases revealed that mild cases tend to clear the of-care test, less expensive and yields quicker results
viruses early, while severe cases can have prolonged viral within minutes. However, there is a higher chance of
shedding [76]. Data from studies using twin respiratory false-negative results as compared to molecular testing.
and fecal sampling have shown viral shedding can persist Molecular testing yields more accurate results but are
in stools for more than 4 weeks even when respiratory time-consuming [79].
samples are negative [77]. Transmission during the
asymptomatic phase has also been reported. In a study TREATMENT
from Singapore, 6.4% of the 157 locally acquired cases of
Initially, early in the pandemic, the understanding of
COVID-19 were attributed to transmission during the
COVID-19 and its therapeutic management was limited,
asymptomatic phase of the disease [78].
creating an urgency to mitigate this new viral illness with
experimental therapies and drug repurposing. Since then,
DIAGNOSIS
due to the intense efforts of clinical researchers globally,
significant progress has been made which has led to a
When is a COVID 19 diagnostic test required?
better understanding of not only COVID-19 and its
Diagnostic testing for COVID-19 is conducted to find out management but also has resulted in the development of
whether a person is infected with the SARS-CoV-2 virus, novel therapeutics and vaccine development at an
responsible forCOVID-19 infection. Your healthcare unprecedented speed [80].
practitioner may recommend you the same if:
PREVENTION
• You are experiencing symptoms of COVID 19 such as
high fever, cough, shortness of breath, excessive Preventive measures are the current strategy to limit the
fatigue, etc. spread of cases. Early screening, diagnosis, isolation, and
• You have long-term health conditions such as asthma, treatment are necessary to prevent further spread.
heart diseases, etc. and experience a sudden Preventive strategies are focused on the isolation of
worsening of symptoms. patients and careful infection control, including
• You have come in contact with someone tested appropriate measures to be adopted during the diagnosis
positive for COVID 19 recently. and the provision of clinical care to an infected patient
• You are a healthcare worker working in a hospital [81]. Important COVID-19 prevention and control
environment. measures in community are summarized in Table 1.
• You require hospitalization for treatment or surgery Table 1: COVID-19 prevention and control measures
of existing medical conditions. in community.

What are the different laboratory tests available to

diagnosis COVID 19?
In general, there are two types of tests for diagnosing
COVID-19 namely, Antigen or rapid testing and Molecular

Quarantine Other Measures

Voluntary quarantine (self-quarantine) Avoiding crowding

Mandatory quarantine Hand hygiene

Private residence Isolation

Hospital Personal protective equipment

Public institution School measures/closures

Others (cruise ships, etc) Social distancing

Workplace measures/closures

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