key: cord-0252289-8oiq3z1w
authors: Buowari, D.Y.; Ogundipe, H.D.
title: SEVERE ACUTE RESPIRATORY SYNDROME CORONAVIRUS-2 (SARS-COV-2) INFECTION: AN EPIDEMIOLOGICAL REVIEW
date: 2021-06-03
journal: Ann Ib Postgrad Med
DOI: nan
sha: 1d1466368f7a68c653b8c3e07ea8cc25bfb2ab98
doc_id: 252289
cord_uid: 8oiq3z1w

BACKGROUND: New strains of different organisms, three of which has been caused by betacorona viruses (SARS-CoV, MERS-CoV and SARSCoV- 2) have caused epidemics and pandemics. The COVID-19, caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) started in China in December 2019 has spread globally. Understanding its pattern of spread and how it affects the populace helps to guide formulation of strategies at curbing its spread, managing the disease and allocation of limited resources in tackling the pandemic. METHODOLOGY: This is a review article about the epidemiology of the coronavirus disease -2019 (COVID-19). Various search engines were used to accumulate literature on the topic; these include PubMed, Google scholar, Ajol. RESULTS: As at October 29, 2020, SARS-CoV2 has spread to all continents except the Antarctica. Though a zoonotic disease, human to human transmission has resulted to this pandemic is via direct and indirect contact of droplets with mucosal surfaces. Most severe cases occur among the elderly, males, and people with co-morbid diseases. The average incubation period is 2-10 days. When compared with SARS-CoV (Ro: 2.3-3.7, mortality rate 11%) and MERS-CoV (Ro: 0.8-1.3, mortality rate: 34.3%), SARS-Cov-2 is a highly infective (Ro: as high as 6.5) with low mortality rates (average range mortality rates 1.83- 6.3%). CONCLUSION: COVID-19 is a highly infective novel virus. Older persons and people with medical comorbidities are more susceptible to the severe form of the disease and mortality. As the second wave comes on, a sustainable measure of limiting the spread and consequences of COVID-19 should be more emphasized.

The Zika virus caused an epidemic in Brazil between 2015-2016 with 1,500,000 cases. 10, 11 The virus was named after the zika forest where it was first isolated in Uganda in 1947, it is transmitted through a bite from an infected Aedes mosquito species. 11 The Ebola virus causing Ebola viral heamorrhagic disease derives its name from the Ebola River in the Democratic Republic of Congo, where it was first isolated. It is transmitted to man by eating an infected fruit bat and has caused several sporadic epidemics over the years and has a mortality rate of 90%. The first outbreak of the disease occurred in 1976 in South Sudan and Zaire (now Democratic Republic of the Congo) 12 and the latest occurred between 2014 and 2016. 13 By 2020, three of the epidemics/pandemics so far experienced have been caused by the novel strains of the beta coronaviruses with influenza-like symptoms, the Severe Acute Respiratory Syndrome coronavirus (SARS-CoV), the Middle East Respiratory Syndrome (MERS) and the Severe Acute Respiratory Syndrome coronavirus -2 (SARS CoV-2). 14 SARS CoV caused an outbreak in China in 2002 with pneumonia-like symptoms 15 with 29 countries affected. From 2002 to 2003, there were 8,422 cases and 916 deaths and a mortality rate of 11%. 16 MERS-CoV infected man through direct and indirect contact with dromedary camels and camel products started an outbreak in the Kingdom of Saudi Arabia 2012. [17] [18] [19] . By 2019, it has spread to 5 continents involving 27 countries with 2,499 confirmed cases and 858 deaths and a mortality of 34.5%. 20

The outbreak of COVID-19 originated from Wuhan City, Hubei Province, China in December 2019, when a cluster of patients with pneumonia of unknown cause were managed. It was traced to a seafood market at Wuhan. A novel virus, identified as a type of coronavirus was isolated as the causative organism on January 7, 2020 by Chinese scientists. 21 The interim name 'novel coronavirus 2019' (2019nCoV) was proposed for the vir us by the World Health Organization (WHO) 22 and the definitive name was announced as "severe acute respiratory syndrome coronavirus-2" (SARS-CoV-2) by the International Committee on Taxonomy of Viruses (ICTV) in March 2020. 23 The pneumonia resulting from this viral infection has been named COVID-19 (coronavirus disease 2019) by WHO in February 11 2020. 24 The WHO also declared it as a Public Health Emergency of International Concern (PHEIC) on January 30, 2020, and as a pandemic in March, 2020 as it spread round the world. 22

COVID-19 has affected 216 countries and territories globally and 2 international conveyances 25 . According to WHO, as at 29th October 2020, COVID-19 has caused a total of 44,002,003 confirmed cases and 1,167,988 deaths (2.65% case fatality rate) reported worldwide. 26 The Americas (45.5%), Europe (22.5%) and South-East Asia (20.6%) being the continents hardest hit by the pandemic with the United States (19.7%), India (18.3%) and Brazil (12.4%) being the countries most affected with the viral infection and the Antarctica have no reported case. 26 The United States (19.3%), Brazil (13.5%) and India (10.3%) have the highest number of mortalities from the disease. 26 Africa was the last continent to be affected by the Coronavirus, and only accounts for 3% of infections worldwide 26 . The first confirmed cases in Africa was in Egypt on 14th of February, 2020, and did not become wide spread in Africa till mid-March, 2020. Although challenges with knowing the true burden of COVID-19 in the African continent exists due to the inadequate testing capacity for COVID-19 27 review of available studies have noted that COVID-19 concentration in urban areas, among lower socioeconomic status communities, and within congregate living settings. 28 America, Europe and east Mediterranean continents appear to be experiencing a second wave of the infection. 26

Available information on the susceptibility to SARS-CoV-2 infection based on gender is varied across continents; most studies however, show no significant difference in the likelihood of acquiring the infection based on gender. Majority of studies and reviews from China, Japan and studies from Africa showed relatively equal gender distribution or mild male/female preponderance amongst patients infected with coronavirus with the male to female ratio of 0.92-1.4:1. [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] However, isolated studies from China, Africa and available data from Iran noted males were almost three times likely to be infected with SARS-COV 2 with M: F ratio of 1.93-3.25:1. [41] [42] [43] [44] Quite contradictory however, were studies from Korea, Europe and a study from Zhejiang province in China where females were noted to be almost twice likely to be infected with coronavirus with M: F ratio of 0.48 -0.7:1. [45] [46] [47] Annals of Ibadan Postgraduate Medicine. Vol. 19 2021 COVID-19 Supplement

While these variations might be coincidental, they could as well be a result of factors which are not yet known. Could these observed variations be due to the likelihood of involvement with outdoor activities, likelihood to seek health care based on cultural norms as most of these studies are hospital based studies, or is it related to the likelihood of being charged with taking care of ailing family members or neighbours, or could there be some hormonal factors that affect the expression of the receptors for the virus on the mucosal surfaces. These are definitely areas for more research.

All ages are at risk of contracting SARS-CoV-2. However, studies on the epidemiology of COVID-19 are unanimous in finding the middle age group as the predominant age group affected by the viral infection while children and the elderly above 80 years being the age groups which are least likely to harbor the infection. Several studies across all continents have noted that most patients diagnosed with COVID-19 are aged 30-79 years constituting 74.3% -91.2% of confirmed cases. [46] [47] [48] [49] [50] [51] [52] [53] [54] Other studies further confirm that the middle aged groups are the most affected by the coronavirus pandemic 33-36,48 with a mean age range of 38.76 -56.7 years 46,49 and median age range of 41.5 -59 years. 38, 48 COVID-19 in children has been noted to run a milder course than in adults as they are more likely to have asymptomatic, mild or moderate disease, constituting 94.1-100% of COVID-19 cases in children. [50] [51] [52] [53] Children are less likely to have severe disease as they constitute 0-5.9% of severe or critical cases. 50, 51 However, amongst children, infants have been noted to be more likely to have severe disease. Dong et al found that infants constituted 32% of severe and critical cases among COVID-19 cases in children studied in China. 51

Nosocomial transmission to health workers have being a worry as it will affect the number of available frontline health workers in hospitals to care for patients during this pandemic that is constantly overwhelming medical facilities. In China, health care workers constituted 2.4% -4.6% of COVID-19 cases. 49, 54 Infection rates were higher in Europe, in a review of COVID 19 cases across Europe, 30.7 % of infected patients in the study were healthcare workers. 46 Also, health workers constituted 9.2% of COVID-19 infections in Italy 52 Asymptomatic, Mild, Moderate, Severe And Critical Infection COVID-19 is a self-limiting viral infection and it runs a mild course in most patients. 55 Review of studies have demonstrated that more than 80% of patients are asymptomatic or run a mild or moderate disease (81-91% of all cases) with severe and critical disease noted in 7.7 -9.1% of COVID-19 patients. Other studies have found higher rates of severe disease ranging 17.6-22.1% of patients. 56, 57 Severe COVID-19 Disease With any disease, factors associated with severe disease and mortality are of importance, as they form a key concern and as such efforts are concentrated in preventing these outcomes or deciphering effective early intervention to prevent mortality. Such is a key concern with COVID-19. Elderly people, male gender, people with co-morbidities (underlying diseases), and those with compromised immune status have been noted to be more likely to have severe disease. Studies have shown that patients aged 60 years and above, particularly patients above 80years and those with underlying medical comorbidities are more likely to be develop severe disease of COVID-19. 57-60 Pan et al. in a review of epidemiology of COVID cases in Wuhan noted that 41.3% of severe cases occurred among the elderly. 29 Allergic diseases, asthma, and chronic obstructive pulmonary disease (COPD), were also identified as predisposing factors for severe COVID-19 disease. 61 Pregnant women and neonates have also been noted to be more likely to develop severe cases of COVID 19, 59 this is perhaps due to their impaired immune status. Furthermore, the male sex has been found to be more likely to develop severe forms of COVID-19. 34 

Although the overall mortality rate for COVID-19 is low, it has been noted to correlate with the epidemiological dynamics of severe cases, being higher among the elderly, patients with underlying medical conditions and males. In a review of COVID-19 patients male gender, older age, and having underlying diseases were significantly associated with higher mortality. 41, 44 The case fatality rate in China has ranged between 1.83% -4.05%, 54 to 2.6%. [61] [62] [63] [64] However, in a review by Bulut et al., higher values were found 48 . The mean case fatality rate across several countries in Asia, Europe and South America was 6.3% (0.81-15.23%) with the highest fatality rates noted in countries with more elderly patients. 57 Similar age related mortality was also noticed by Wu et al., who found mortality to be closely related with increasing age with a case fatality rate of 14.8% in patients aged >80 years and 35.7% in patients underlying illness. 49 Mortality from COVID-19 in Europe from the most affected countries (France, Italy and Spain) (8.8-15%) was higher than that in observed in China 59, 65 with almost half of the deaths occurring in those older than 80years. 66 Mortality rates in Africa have been observed to be relatively low compared to the rest of the world. with mortality rates majorly less than 5% 44,67 though rates as high as 9-15% have been recorded in few countries. 27, 43 This low mortality rate has been ascribed to several reasons such as effective mitigation measures, population that is more youthful, favorable weather, and possible prior exposure to a cross-reactive virus with Njenga et al noting a youthful population and the favorable weather as the most compelling arguments 68 When compared with similar pandemics caused by viruses in the same family (SARS-CoV and MERS-CoV), SARS-CoV-2 has a lower mortality rate compared to SARS-CoV (11%) 16 and MERS-CoV (34.5%). 20

About 66% patients initially diagnosed with the pneumonia in China had been in contact with the seafood market in Wuhant. 69 The exact animal responsible for transmission of SARS-Cov-2 as well as the specific mechanism of infection/transmission route from animals to human remains unclear. 69 Several reports have suggested different animals such as snakes, birds, bats as reservoirs and intermediate hosts. 64 Bats are considered to be the most likely initial hosts of SARS-CoV-2, while pangolins may be the intermediate hosts. 34 Human to human transmission appears to be the most important route of spread for this pandemic. Evidence in support evolved when several cases of COVID-19 was detected among individuals who had not been to the Wuhan market, among family clusters and among health workers who were caring for COVID 19 patients, as well as clustered infections in work places and public transportation. 70, 71 Human to human transmission occurs through direct or indirect contact with droplets or fomites containing particles of the virus 57,65 produced by coughing or sneezing from infected individuals 64, 72 came in contact with mucous membranes of the eyes, mouth or nose. 59, 73 . Aerosol transmission within the general population has been speculated but review of available evidence remains inconclusive. 56, 57 However within hospital settings, aerosol generating procedures such as nebulization, suctioning, intubation, bronchoscopy and cardiopulmonary resuscitation for COVID-19 patients could lead to spread of the infection. 65 Scientists have discovered that SARS-CoV-2 binds to the ACE2 receptor, which is ubiquitous on human mucosal cells, thus exposed mucosa surfaces like that of nose, eye and mouth have been suggested as the most likely routes of entry of the virus into the human body. 30 Faeco-oral transmission has also been speculated due to identification of the virus in feaces and gastrointestinal secretions, 70, 73 however, the validity of such theories are yet to be ascertained. 56,57 SARS-CoV-2 have also been detected in body fluids/secretions, urine, and tears of infected individuals, ,65,70 though no clear evidence that they can be a source of transmission of infection. There is also no evidence of vertical transmission of SARS-CoV-2 from mother to child. 64, 73 Human to human transmission has been found to occur not only from symptomatic patients but also from asymptomatic individuals 58,72 who may not be even aware that they harbor the viral infection. Study of COVID-19 patients revealed that there is no difference in the viral load of asymptomatic and symptomatic patients; suggesting risk of transmission from asymptomatic individuals. 30 Du et al also noted that 13% of patients in their study were contagious before being symptomatic. 74 Healthcare workers exposed to COVID-19 patients and family members of COVID-19 patients appears to have the highest risk of contracting the disease due to their increased contact with the patients. 34

Several studies on the incubation period and the reproductive rate of the SARS-CoV-2 virus are aimed at determining the period of isolation of infected individuals and quarantine of contacts, determine the infectivity of the virus and monitor the rate of spread of the disease. The basic reproduction number (Ro), is the average number of secondary cases generated by an infectious case. As long as the Ro is more than 1, human-to human transmission would persist. The aim at flattening the curve of transmission is for Ro to be less than 1.

Ro estimates from several studies were 1.4 to 6.49. , 61, 75 In a review of 21 estimates for the Ro, it ranged from Annals of Ibadan Postgraduate Medicine. Vol. 19 2021 COVID-19 Supplement S72 1.9 to 6.5, but majority (62%) of estimates were between 2.0 and 3.0. 62 The average Ro from reviews worldwide (2-6.47) 76-78 is comparable to data from China (1.4 to 5.7), 57,61 South Africa (2.95), 79 Italy (2.5 -3.6), 66, 80 other European countries (3.1 to 6.56). 57 Cold and dry conditions have been noted as potentiating factors for the spread of the virus. 81 SARS-CoV-2 has a significantly higher infectivity rate compared to other epidemic/pandemic causing viruses in the same family (SARS-CoV (Ro: 2.3-3.7) and MERS-CoV (Ro: 0.8-1.3) that have caused epidemics in humans. 33, 78 Incubation Period Global review of estimates the incubation period of SARS-CoV-2 varied, but most studies reveal values which ranged between 2 -10 days with average incubation periods of 5-7days. , 77, 82 Several studies further documented 14 days as the upper limit of the incubation period. ,71,72 However longer incubation periods, 19-27 days, have been reported. [84] [85] [86] Prevention of SARS-CoV-2 Ro estimates in China were found to reduce to below 1 with rapid diagnosis and isolation of infected patients. 61 Similar findings were noted by Zindonga et al. with 80.31% reduction in infection rate of COVID-19 after institution of lockdown in South Africa. 79 The use of facemask, hand hygiene, social distancing, isolation of infected patients have been associated with decrease in spread of the coronavirus. , 87, 88 The most consistently effective measure in reducing risk of SARS-CoV-2 infection being the use of face masks risk. 89 Derek et al. in a systematic review noted that the transmission of viruses was lower with use of facemasks, eye protections and maintaining physical distancing of 1 m or more. 90 Amongst health workers, there is clear association between the use of personal protective equipment (PPE) (facemasks, gloves, gowns, eye protection, shoe covers) and decreased risk for nosocomial transmission of SARS-CoV-2 infections. Infection control training and education also helped reduce transmission. Inadequacy of PPE supplies is associated with increased risk for infections for health care workers. 89 CONCLUSION COVID-19 is a highly infective novel virus with varying incidence in difference countries and has low mortality. Older persons, males and people with medical comorbidities are more susceptible to the severe form of the disease and mortality from the disease. Use of facemasks and eye shields, regular hand hygiene and maintaining social distance of at least 1 metre are effective measures in limiting the spread of SARS-CoV-2? As the second wave comes on, should lockdown be considered as a sustainable measure of limiting the spread of COVID-19 or should more emphasis be laid on enforcing preventive measures and putting in place modalities for early identification and treatment for the population with highest risk of severe disease and mortality from SARS-CoV-2. Given the highly infective nature of this viral infection and the absence of vaccine, maintaining a flattened curve may be a challenge, perhaps impossible. Reducing the transmission with preventive measures compatible with daily activities and reducing mortality from the disease is more feasible and practical and efforts should be moulded in that direction.

Funding None

The classical definition of a pandemic is not elusive

Nonpharmaceutical measures for pandemic influenza in nonhealthcare settings personal protective and environmental measures. Emerging Infect Dis

The pandemic and its impacts. Health, Culture Society

World Health Organization. WHO outbreak communication. WHO handbook for journalists. Influenza pandemic

The 1918 Spanish flu pandemic, the origins of the HIN 1 -virus strains, a glance in history

A review on study of swine flu. Indo-global research

Swine flu and current influenza a (HIN 1) pandemic in humans: a review

A review on zika virus outbreak epidemiology, transmission and infection dynamics

Zika virus disease

World Health Organization. Introduction to Ebola disease. Manag Infect Dis

The spread of the Ebola virus disease and its implications in the West African sub-region

influenza: the mother of all pandemics. Emerging Infect Dis. www.cdc.gov/eid

The emergence of Middle East Respiratory Syndrome coronavirus. Pathogens Dis

Consensus Document on the Epidemiology of Severe Acute Respiratory Syndrome. World Health Organization

Outbreak of Middle East Respiratory Syndrome coronavirus in Saudi Arabia: a retrospective study

Retrospective, epidemiological cluster analysis of the Middle East Respiratory Syndrome coronavirus (MERS-CoV) epidemic using open source data

Middle East Respiratory Syndrome

World Health Organization. WHO MERS Global Summary and Assessment of Risk

The continuing 2019-nCoV epidemic threat of novel coronaviruses to global health. Novel coronavirus outbreak in Wuhan

Novel Coronavirus (2019-nCoV) Situation Report 10

The species severe acute respiratory syndrome-related coronavirus: classifying 2019-nCoV and naming it SARS-CoV-2

Naming the coronavirus disease (COVID-19) and the virus that causes it

WHO Coronavir us Disease (COVID-19) Dashboard

COVID-19 pandemic: An African perspective. Emerging Microbes Iinfections

COVID-19 Across Africa: Epidemiologic Heterogeneity and Necessity of Contextually Relevant Transmission Models and Intervention Strategies

Association of Public Health Interventions With the Epidemiology of the COVID-19 Outbreak in Wuhan, China

COVID-19 epidemic: Disease characteristics in children

The Novel Coronavirus Pneumonia Emergency Response Epidemiology Team. The Epidemiological Characteristics of an Outbreak of

Novel Coronavirus Diseases (COVID-19) China

Characteristics of COVID-19 infection in Beijing

Zhonghua liu Xing Bing xue za zhi = Zhonghua Liuxingbingxue Zazhi

An overview of COVID-19

Epidemiology and transmission of COVID-19 in 391 cases and 1286 of their close contacts in Shenzhen, China: a retrospective cohort study

National Task Force for COVID-19 Outbreak in Japan, Epidemiology of COVID-19 Outbreak in Japan

The Late Arrival of Coronavirus Disease

Early Transmission Dynamics in Wuhan, China, of Novel Coronavirus-Infected Pneumonia

Epidemiological and clinical features of 125 Hospitalized Patients with COVID-19 in

Current epidemiological and clinical features of COVID-19; a global perspective from

Epidemiological characteristics of coronavirus disease 2019 (COVID-19) patients in IRAN: A single center study

Understanding of COVID-19 based on current evidence

Epidemiology of novel COVID-19 in Nigeria. Microbes and Infectious Diseases

Descriptive epidemiology of coronavirus disease 2019 in Nigeria

Korean Society for Antimicrobial Therapy, Korean Society for Healthcare-associated Infection Control and Prevention

Clinical and epidemiological characteristics of 1420 European patients with mild to moderate coronavirus disease 2019 (Original article)

Epidemiologic and clinical characteristics of 91 hospitalized patients with COVID-19 in Zhejiang, China: a retrospective, multicenter case series

Epidemiology of COVID

Asymptomatic and Pre-Symptomatic COVID-19 in China

Clinical and epidemiological features of 36 children with coronavirus disease 2019 (COVID-19) in Zhejiang, China: an observational cohort study

Epidemiology of COVID-19 among Children in China

COVID-19 in children and adolescents in Europe: a multinational, multicentre cohort study

Diagnosis, treatment, and prevention of 2019 novel coronavirus infection in children: experts' consensus statement

Epidemiology Working Group for NCIP Epidemic Response, Chinese Center for Disease Control and Prevention

COVID-19 in a tertiary hospital from Romania: Epidemiology, preparedness and clinical challenges

Unique epidemiological and clinical features of the emerging 2019 novel coronavirus pneumonia (COVID-19) implicate special control measures

Epidemiology and clinical characteristics of COVID-19

Current Status of Epidemiology, Diagnosis, Therapeutics, and Vaccines for Novel Coronavirus Disease 2019 (COVID-19)

Coronavirus disease 2019 (COVID-19): current status and future perspectives

The COVID-19 Pandemic: Public Health and Epidemiology

COVID-19: Epidemiology, Evolution, and Cross-Disciplinary Perspectives

A Systematic Review of COVID-19 Epidemiology Based on Current Evidence

The COVID-19 Pandemic: A Comprehensive Review of Taxonomy, Genetics, Epidemiology, Diagnosis, Treatment, and Control

The epidemiology and pathogenesis of coronavirus disease (COVID-19) outbreak

Severe Acute Respiratory Syndrome Coronavirus as an Agent of Emerging and Reemerging Infection

COVID-19 working group. Epidemiological characteristics of COVID-19 cases in Italy and estimates of the reproductive numbers one month into the epidemic

Epidemiology of COVID-19 in Africa: daily cumulative index and mortality rate

Why is There Low Morbidity and Mortality of COVID-19 in Africa? Am

The epidemiology and clinical information about COVID-19

COVID-19 (Novel Coronavirus 2019) -recent trends

Coronavirus disease 2019 (COVID-19): A literature review

A Review of Coronavirus Disease-2019 (COVID-19)

COVID-19: a review. Monaldi Archives for Chest Disease

Serial interval of COVID-19 among publicly reported confirmed cases. Emerging Infectious Dis

The epidemiology and clinical information about COVID-19

The epidemiology, diagnosis and treatment of COVID-19

Epidemiology, causes, clinical manifestation and diagnosis, prevention and control of coronavirus disease (COVID-19) during the early outbreak period: a scoping review

The reproductive number of COVID-19 is higher compared to SARS coronavirus

Quantifying early COVID-19 outbreak transmission in South Africa and exploring vaccine efficacy scenarios

Spread and dynamics of the COVID-19 epidemic in Italy: Effects of emergency containment measures

Effects of temperature and humidity on the spread of COVID-19: A systematic review

World Health Organization declares global emergency: A review of the 2019 novel coronavirus (COVID-19)

Epidemiology and clinical features of COVID-19: A review of current literature

The COVID-19 epidemic

/uri>) which permits unrestricted, non-commercial use,distributionand reproduction in any medium

Presumed asymptomatic carrier transmission of COVID-19

The Incubation Period of Coronavirus Disease

From Publicly Reported Confirmed Cases: Estimation and Application

Advice on the use of masks in the context of COVID-19 Interim guidance

Advice on the use of masks in the context of COVID-19 Interim guidance

Epidemiology of and Risk Factors for Coronavirus Infection in Health Care Workers: A Living Rapid Review

on behalf of the COVID-19 Systematic Urgent Review Group Effort (SURGE) study authors. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis