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 Table of Contents  
REVIEW ARTICLE
Year : 2020  |  Volume : 11  |  Issue : 2  |  Page : 71-76

A panoramic view of COVID-19: Epidemiology and challenges


Department of Community Medicine, Father Muller Medical College, Mangalore, Karnataka, India

Date of Submission04-Jun-2020
Date of Acceptance26-Aug-2020
Date of Web Publication25-May-2021

Correspondence Address:
Dr. Anissa Mary Thomas Thattil
Department of Community Medicine, Father Muller Medical College, Mangalore - 575 002, Karnataka
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mjmsr.mjmsr_23_20

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  Abstract 


The rise of a novel disease agent is a complex situation that is fraught with fear and concern. The SARS-CoV-2 novel virus was identified in the Hubei province of China in December 2019, and since then, its rapid spread has become a matter of international concern. For this article, a literature search for the origin of the virus, mortality and morbidity data, pandemic influenzas in the past, modes of transmission, incubation period, vulnerable populations and clinical features, was conducted. Although evidence regarding the epidemiology of the disease is not thorough and is being studied further, this article aims to collate existing data and understand the epidemiology of COVID-19 while also trying to identify the global challenges that will have to be faced in the near future.

Keywords: COVID-19, epidemiology, pandemic, SARS


How to cite this article:
Fernandez R, Roshan NS, Thattil AM. A panoramic view of COVID-19: Epidemiology and challenges. Muller J Med Sci Res 2020;11:71-6

How to cite this URL:
Fernandez R, Roshan NS, Thattil AM. A panoramic view of COVID-19: Epidemiology and challenges. Muller J Med Sci Res [serial online] 2020 [cited 2021 Jun 23];11:71-6. Available from: https://www.mjmsr.net/text.asp?2020/11/2/71/316691




  Introduction Top


The World Health Organization (WHO) has defined a pandemic as “the worldwide spread of disease” and the COVID-19 pandemic has become the defining health problem of our time.[1] It also has the potential and is already impacting the global economy adversely.[2] The SARS-CoV-2 virus causing COVID-19, is believed to have originated from a wet-market, which provides a perfect human-animal interphase, leading to the emergence of novel viruses.[3] The inter-species jump of these viruses are unpredictable and their complex pathway leading to the emergence of a pandemic virus, is yet to be understood. The COVID-19 pandemic is proving to be a challenge to overcome, and cognizance of its epidemiology is one of the first steps.


  Methodology Top


A literature search was conducted in “PubMed,” “Google Scholar,” and the Goggle search engine, which comprised of the following terms in various combinations “COVID-19,” “coronavirus,” “SARS-CoV-2, “pandemic,” “One health,” “pollution,” and “novel virus.” All articles up to May 17, 2020, were selected. Further, a literature review through hand searches in WHO and CDC websites were also conducted. The references cited in the various selected articles were scrutinized and topics pertinent to this review were chosen. Data were extracted from the selected literature that contained information regarding the origin of the virus, mortality and morbidity data, pandemic influenzas in the past, modes of transmission, incubation period, vulnerable populations, and clinical features.


  Origin of the Severe Acute Respiratory Syndrome Coronavirus 2 Top


In December 2019, pneumonia cases of unknown etiology were identified in the city of Wuhan, in the Hubei province of China. Many of these patients gave a history of having visited a seafood and wildlife market and retrospective investigations confirmed the presence of a local outbreak, with cases surfacing since early December 2019.[4],[5] Subsequently, the viral nature of the disease was established; it was caused by a new type of coronavirus called 2019-nCoV. The virus was thereafter renamed as Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and the disease was called COVID-19, by the WHO.[6] The first case outside China was reported on January 13, when a Chinese resident was diagnosed in Thailand. By January 23, 29 provinces including 6 other countries (France, Thailand, Japan, South Korea, USA, and Taiwan) reported 846 confirmed cases. The imposition of a lockdown in Wuhan city coincided with the Chinese New Year and an estimated 5 million people had already travelled out of the city. With the rapid rise in the number of cases, the WHO declared a Public Health Emergency of International Concern on January 30, 2020, and on March 11, 2020, the status of a pandemic was confirmed. The SARS-CoV-2 is the seventh virus in the Coronaviridae family to cause disease among humans.[4]

The ecological origin of the virus has been traced back to bats, similar to that of other coronaviruses, with an 89%–96% genomic similarity to bat coronaviruses.[7] Samples that were taken from the Wuhan market tested positive for the virus, implying that the market was either the point of the virus origin, or else played an amplifying role in the spread of the disease.[5] Although preliminary investigations suggested that the virus may have been transferred from bats to humans, it is highly likely that other animal species (domestic, wild or domesticated wild) may also have played an intermediate role in the transmission of the virus.[4],[5] This possible inter-species spread, might have been enhanced by the crowded nature of the open market. Further, all known genomic evidence shows that the virus is of natural animal origin and has not been created artificially.[5] The SARS-CoV-2 belongs to the beta-coronavirus genus and can bind to the human angiotensin-converting-enzyme 2 receptor.[4],[8]

Globally, COVID-19 has affected 216 areas or territories, with more than 4.5 million people infected and more than 300,000 deaths (as of May 17, 2020).[9] India reports more than 90,000 active cases and more than 2000 deaths, according to the Ministry of Health and Family Welfare, Government of India (as of May 17, 2020).[10] The case fatality rate (CFR) of the COVID-19 infection is at 6.8% as of March 17, 2020.[9] This is lower than previous coronavirus epidemics, such as SARS 2003 (CFR: 15%) and Middle East Respiratory Syndrome Coronavirus (MERS-CoV) (CFR: 35%).[11],[12] An important point to consider is that, the CFR varies with the health system capacity of the country and access to health resources.[13]

[Figure 1] compares the morbidity and mortality data across countries, while [Figure 2] depicts the Indian states with the highest morbidity and mortality from COVID-19. [9],[14]
Figure 1: Global COVID-19 morbidity and mortality statistics as of May 17, 2020

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Figure 2: States with the top 10 COVID.19 morbidity and mortality data in India as of May 17, 2020

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  Lessons from History Top


Due to the similarities within the beta-coronavirus genus, such as SARS-CoV-1, MERS-CoV, and SARS-CoV-2, our understanding of previous pandemics is crucial in the control and prevention of COVID-19.

Spanish Flu/H1N1 Flu pandemic (1918)

The Spanish Flu was caused by an H1N1 virus of avian origin which spread globally between 1918 and 1919. Although the geographical origin of the virus has not been identified till date, the virus was initially isolated from among the US military personnel. One of its unique characteristics was the very high mortality rate among healthy adults between the ages of 15 and 34 years. Although the Spanish Flu and SARS-CoV-2 are transmitted through droplet particles, they differ from each other in the fact that the former affects people of all age groups equally whereas the latter severely affects age groups between 41 and 60 years.[15] A pandemic with such a high mortality rate, is yet to be observed.

Asian Flu (1957–1958)

This pandemic was caused by influenza A (H2N2) which emerged in East Asia.[16] Within a year, the H2N2 virus had replaced the previously circulation strains of the H1N1 virus from 1918.[17] Transmission to humans occurred via the eyes, nose, or the mouth through droplet particles.[18] The first case was identified in Singapore. Globally, this pandemic claimed 1.1 million lives.[16] Almost 10 years later, the H2N2 virus was replaced by the H3N2 virus.

H3N2 virus pandemic (1968)

Also called the Hong Kong pandemic, this was caused by Influenza A (H3N2) which contained certain components of the 1957 H2N2 virus.[17] It caused almost 1 million deaths worldwide, affecting mostly people of the age 65 years and older. This virus continues to circulate globally as seasonal Influenza A virus.[19] The infection causes upper respiratory symptoms such as fever, chills, weakness, and myalgia, persisting for 4–6 days.[20]

Severe Acute Respiratory Syndrome (2003)

SARS was the first pandemic of the 21st century. It was caused by a coronavirus called SARS-CoV-1 which was isolated from bats and infected civets before reaching humans.[21] SARS-CoV-2 is however thought to have originated in bats, infected pangolins, and later humans. The SARS-CoV-2 virus phylogenetically belongs to the same family as the SARS-CoV-1 virus.[7] Although both are spread through droplet infection, and both affect older adults more frequently and severely, SARS-CoV-1 only spread to five countries (Hong Kong Special Administrative Region of China, Toronto in Canada, Singapore, Chinese Taipei, Hanoi in Viet Nam) and affected only around 8000 people in total.[22] The impact of COVID-19 has already surpassed that of SARS 2003.

H1N1 (2009)

The 2009 pandemic was caused by the Influenza A virus. Since the virus contained genes that were not identified previously in humans or animals, it was designated as Influenza A (H1N1) pdm09 virus. The virus was initially detected in the US and affected individuals of all ages, with more than 80% of the mortality having occurred in individuals < 65 years of age. Some older adults exhibited antibodies against this virus, which was indicative of previous exposure to a similar virus in their past, presumably the 1918 virus.[17],[23]

Middle East Respiratory Syndrome (2012)

The MERS is caused by a coronavirus known as the MERS-CoV. The virus is believed to have originated in bats and transmitted to humans through contact with dromedary camels. Retrospective studies identified the first known case in Jordan and all known cases were linked to countries in and around the Arabian Peninsula; however, the Republic of Korea reported an outbreak in 2015. MERS-CoV is transmitted through close contact and nosocomial transmission has also been reported. Asymptomatic individuals have tested positive for MERS-CoV, which has also been reported in COVID-19.[12],[24]

[Figure 3] provides a graphical comparison of the deaths due to previous pandemics with that of COVID-19.
Figure 3: Comparison of mortality data of previous pandemics with COVID-19. *Data as of May 17, 2020, ^deaths since 2012

Click here to view


Experience with the SARS-CoV-1 and MERS-CoV pandemics shows that coronaviruses can “spillover,” i.e., they can cross the inter-species barrier from animals to humans.


  Epidemiological Factors Top


There are several determinants that have been identified as influencers in the pandemic. These are:

  1. Age and immune status: COVID-19 appears to be rare in children with mild symptomatology among those who acquire the disease. Individuals > 60 years of age, immunocompromised persons and those suffering from chronic diseases (such as cardiovascular disease, hypertension, diabetes, chronic respiratory diseases, obesity, chronic renal, or liver disease) were found to be at higher risk of severe disease and progression to death. In addition, smoking, bone marrow or organ transplantation and persons living with poorly controlled HIV/AIDS were found to be at increased risk of COVID-19[7],[25],[26],[27]
  2. Pregnancy: Pregnant women are not at greater risk of severe disease, however those aged >35 years, overweight/obese and suffer from preexisting medical conditions such as hypertension and diabetes, are at an increased risk[28]
  3. Place of residence: Population density is directly associated with the spread of disease, thus, individuals living in urban areas are at higher risk that their rural counterparts. Households that have more members living together, are at increased risk of transmitting the disease to another family member[29]
  4. Socioeconomic factors: As the COVID-19 is transmitted through droplets, individuals from lower socio-economic strata might be disproportionately affected, due to greater proximity of people and poorer levels of hygiene and inequitable access to healthcare.[29] Religious views, education and digitalization are also crucial determinants in health outcome as they determine an individual's attitude toward government rules, lifestyle and health behaviors that are adopted, to reduce disease transmission[30],[31]
  5. Health-care infrastructure: This defines the quantity and quality of the health-care services that are delivered. It also describes the testing and reporting ability of a country. Countries with well-structured health systems are able to positively deal with pandemics[32],[33]
  6. Population health: Susceptibility to disease is also determined by the physical and mental state of a person. A more severe consequence can be expected in countries that have a higher prevalence of preexisting diseases[32]
  7. Environmental pollution: Evidence indicates that there is an association between air pollution and COVID-19 disease outcomes. Countries with increased air pollution have been found to have increased vulnerability to epidemic outbreaks.[34]



  Modes of Transmission Top


The WHO reports that SARS-CoV-2 is transmitted through respiratory droplets and through contact. Droplet transmission takes place within 1 meter of an individual exhibiting respiratory symptoms such as coughing and sneezing. The droplets can enter via the oral or nasal mucosa or conjunctiva of the susceptible individual. As the droplets are heavy, they do not remain suspended in air, but fall to the ground in the vicinity of the point of generation.[25] Although transmission from asymptomatic individuals during the incubation period has been reported, evidence is inconclusive.[35],[36],[37] Transmission can also take place indirectly through objects that were used by the infected individual. Evidence shows that SARS-CoV-2 can survive on stainless steel and plastic surfaces for up to 3 days, less than a day on cardboard and <4 h on copper.[25] Airborne transmission is also possible in certain procedures or support treatments which generate aerosols. Prolonged contact has been found to have the highest risk of transmission, rather than casual contact.[38] Nosocomial transmission, as was seen with MERS-CoV and SARS-CoV-1, also has to be taken into consideration.[39] Although the virus has been isolated from fecal samples, feco-oral transmission has not been confirmed to date.[40]


  Incubation Period and Clinical Features Top


Incubation period is the time interval between exposure to an infection and the onset of symptoms. For COVID-19, this period ranges from 2 to 14 days and the median incubation period is 5.5 days.[25],[41] The WHO reports that 82% of patients with COVID-19 suffered mild symptoms and recovered completely. The median time from the onset to symptoms to recovery ranges from 2 weeks in mild cases to 3–6 weeks in severe cases of COVID-19.[26]

COVID-19 presentations range from asymptomatic/mild symptomatology to severe illness and death. The most common symptoms that have been reported include fever, cough, shortness of breath, and malaise. Nonrespiratory symptoms include diarrhea, taste and olfactory disturbances, cardiovascular events, and ocular manifestations (chemosis, conjunctival hyperemia).[25],[42],[43] There is no confirmatory evidence of disease transmission from asymptomatic individuals; transmission can take place from individuals who have a mild cough but do not feel ill.[25],[35],[36],[37]


  Challenges in the Face of COVID-19 Top


The impact of the COVID-19 pandemic is still unfolding. A robust and flexible surveillance system is considered to be the crucial component in the fight against the pandemic. These systems must be established even in areas that have few or nil cases; the health system must be primed to react rapidly in the event of new clusters.[44] In addition, such a system provides reliable data for epidemiologists to identify lacunae in the transmission dynamics of the disease and encourages decisions that are evidence based.[13] Digitalization of data will greatly aid in rapid analysis and data dissemination and all efforts must be made toward the same.

The formulation of sensitive indicators will assist in ensuring quality in the diagnosis and management of cases, along with measures for contact tracing and sufficient quarantine facilities. Evidence from various countries that have overcome this pandemic, show that aggressive measures such as contact tracing, quarantine, isolation, and social distancing, are effective in reducing transmission. Although major efforts are being made to develop a vaccine, it is likely that this process might take anywhere from 12 to 18 months.[45]

The concept of One Health recognizes that human and animal health is closely linked to the ecosystem. This concept has gained more importance, in the light of various zoonotic diseases, including COVID-19. The threat of future zoonotic diseases still looms large, due to population explosion, urbanization, climate change, rapidly evolving microorganisms as well as changing agricultural and animal farming practices. It is imperative that animal and human health sectors collaborate so as to prevent and mitigate the effect of emerging zoonotic diseases.[3] Countries must consider the adoption of the One Health approach for countering future pandemics that are bound to emerge.

Finally, governments must also realize that they have a unique responsibility to balance the civil liberties of its citizens along with the imposition of the necessary control and preventive measures to stop the pandemic.[13] Risk communication plays an extremely important role. Honest and up-to-date information when made available to the public will bolster community participation and curb the spread of misinformation. Interactive, transparent, and nuanced messages must be utilized to promote culturally-sensitive community participation.[46] The cost of dealing with a major pandemic such as COVID-19 will always outweigh the price of preparedness. The inter-connectedness of the world makes collaboration a crucial element in pandemic influenza preparedness. It is essential that countries invest in building a strong prevention and preparedness strategy by strengthening health systems in toto.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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