COVID-19: An Epidemiologic Review

Pneumonia coronavirus covid-19 with noise for illustration
As uncertainty remains and data continues to be collected, the lack of effective drugs to treat coronavirus disease 2019 (COVID-19) suggest that the implementation of infection control interventions is needed.

As uncertainty remains and data continues to be collected, the lack of effective drugs to treat coronavirus disease 2019 (COVID-19) suggests that the implementation of infection control interventions is needed to effectively limit droplet, contact, and fomite transmission and slow the spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), according to a review published in the Journal of Microbiology, Immunology and Infection. These infection control interventions include early identification of patients with SARS-CoV-2 infection and their contacts, avoiding close contact with people with airway symptoms, appropriate hand washing, and enhanced standard infection prevention, and control practices in the healthcare setting

In December 2019, an outbreak of pneumonia due to a novel coronavirus (later named SARS-CoV-2) in Wuhan, China rapidly spread throughout the country within 1 month; the associated disease with SARS-CoV-2 infection was termed COVID-19. On January 30, 2020, the World Health Organization (WHO) declared that the COVID-19 outbreak was the 6th public health emergency of international concern that required a coordinated international response. However, there is still uncertainty regarding important factors associated with COVID-19, including incubation period, clinical features, optimal treatment, and age and sex distribution. Therefore, this literature review focused on compiling the epidemiologic characteristics and clinical manifestations of COVID-19.

COVID-19 was defined as a respiratory disease caused by SARS-CoV-2 and clinical manifestations are protean, which include asymptomatic carrier, acute respiratory disease, and pneumonia of varying degrees of severity. As of February 21, 2020, WHO data revelated a total of 76,769 cases of COVID-19 resulting in 2247 deaths with 32 countries or regions having reports of confirmed cases. However, it is expected that these numbers are an underestimation of the burden of COVID-19 due to asymptomatic patients or patients with mild COVID-19 symptoms who may not seek health care or receive testing for confirm diagnosis. Furthermore, this data shows an overall mortality rate for COVID-19 of 2.9%.

The WHO currently reports the mortality rate to be 2.9%. However, over the course of the pandemic this number has significantly varied. Studies have shown overall mortality ranging from 1.4% to 15%; these large ranges may be due to the study population, differences in disease severity studied, and incomplete outcome measurements due to many patients remaining hospitalized before results were published.

Studies have demonstrated that COVID-19 can affect patients of all ages, may have a high prevalence in men, and that 20% of COVID-19 cases had underlying diseases, with the comorbidities being associated with the more severe cases; the most common underlying condition was hypertension, followed by diabetes. Several studies have established a median age of 47 to 55 years for patients with COVID-19. The largest study conducted in China showed that 0.9% of patients with COVID-19 were aged < 10 years. However, the researchers highlighted that these conclusions require further investigation.

The most common symptoms were fever and cough. One study that included 970 patients showed 44.7% with fever, and roughly 66% with cough; another study that included 468 patients showed results of 76.3% and 70.5%, respectively. Moreover, these 2 studies also showed gastrointestinal symptoms in a range of 5% to 8%.

Determining an accurate incubation period is essential for infection control and guidance for the duration of isolation. Studies have produced various incubation periods ranging from 3.0 days to 24 days. However, larger samples of patients with COVID-19 are needed to determine the infectious period and to determine whether transmission can occur from asymptomatic individuals during the incubation period.

Of the 1099 cases of acute respiratory disease related to COVID-19 investigated, 162 (14.7%) patients had an abnormal chest radiograph. Conversely, 840 (76.4%) patients had abnormal and diverse chest computed tomography (CT) images; the most common CT abnormalities observed were ground-glass opacity (550 [65.5%] patients), local patchy shadowing (409 [48.7%] patients), and interstitial abnormalities (143 [17.0%] patients). In addition, 505 (50.1%) patients had bilateral involvement. However, the resolution of ground glass opacities and a small fibrous stripe may be associated with improvement in the patient’s condition.

Although several reports suggest there are potential drug candidates to treat COVID-19, there is no evidence on clinical effectiveness of these drugs. Of these candidates, remdesivir appears to be the most promising and 2 large clinical trials investigating remdesivir for the treatment COVID-19 ( identifiers: NCT04252664 and NCT04257656, respectively) are underway.

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Overall, the review authors concluded that, “Currently, effective infection control intervention is the only way to prevent the spread of SARS-CoV-2.”


Lai C, Liu YH, Wang C, et al. Asymptomatic carrier state, acute respiratory disease, and pneumonia due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2): facts and myths [published online March 4, 2020]. J Microbiol Immunol. doi:10.1016/j.jmii.2020.02.012.