COMMENTARY: The Infectivity Of COVID-19; Understanding its Virulence

Eleanor Frederick

by Eleanor Frederick, MSc, MPH

COVID-19 is described as “insidious” because many infected people are well enough to go about their daily business unwittingly spreading the disease to others. The World Health Organization (WHO) has defined four transmission scenarios:

No cases
Sporadic cases one or more locally or imported
Cluster of cases
Community transmission


COVID-19 has the potential to affect anyone and everyone, males and females of all age ranges: from infants to the elderly.  The majority of cases however, are seen among those 60 years and older, those who are immuno-compromised and those with co-morbidities. Generally, there are more cases of COVID-19 among men than women.

As the novel coronavirus makes its way across the globe there is a pattern: more men are affected than women and men are more likely to be diagnosed with the severe form of the illness and die. Dr. Deborah Brix , White House Coronavirus Response Coordinator states “this is to all our men out there, no matter what age group: if you have symptoms, you should be tested”.

Data from 1.5 million tests done in the United States (US) showed that 56% of those tested were women and 44% were men. Of those women 16% tested positive and 23% of the men tested positive. A study in Italy revealed that 82% of critically ill patients were men and a study in China had a case fatality rate of 2.8% in men and 1.7% in women.

From that study in the US it seems that men are less likely to try to get tested for the virus when they feel sick. However, based on other diseases and health conditions I believe it can be said that men in general are less likely to present themselves to their healthcare providers to seek testing, care or medication until their conditions worsen as compared to women.

So as the number of cases of coronavirus passes two million and it is believed that the number of cases is much higher due to lack of testing and reporting in many regions, the question should be asked:  Why are so many people of color and by extension men of color the face of COVID-19 positive cases and death? According to the Center for Disease Control (CDC) in the US:

13% of the US population are African Americans
50% of the African American population are more likely to have heart disease than white people
40% of African Americans are more likely to die at an early age from any cause and
19% of African Americans could not afford to see a doctor

Some key epidemiological questions about COVID-19 are:

What is the full spectrum of disease severity?

The full spectrum of disease severity ranges from:

Symptomatic but mild
Severe, requiring hospitalization

How transmissible is the virus?

The virus is easily transmitted and is very contagious. The virus is transmitted from one person to another before and during the first appearance of symptoms.

What role do asymptomatic and pre-symptomatic infected persons play in transmission?

Five to six days is the estimated median time between infection and the onset of symptoms. Some of those who are infected including children do not develop any symptoms. Some studies suggest that symptoms can appear as soon as three days post exposure or as late as thirteen days post exposure.

A study of 191 patients in China found that the median duration of infectiousness was 20 days to a maximum of 37 days. A Japanese study suggested that a substantial proportion of infections are spread by people before they become ill. This can make it difficult to effectively conduct contact tracing during the infectious period so that precautions can be taken against further spread of the disease.

What is the relationship between viral load and disease severity?

Viral load is the key to virulence of COVID-19. In a prospective study similar to SARS in 2002 and 2003 patients with severe COVID-19 tend to have a high viral load and a long virus-shedding period (where the virus leaves a cell to either infect other cells in the body or those in other people) especially in the throat and lungs.

In a study of 76 patients, 30 with severe disease and 46 with mild disease, the mean viral load of severe cases was approximately sixty times higher than that of mild cases. Ninety percent (90%) of mild cases were repeatedly testing negative on RT-PCR by day 10 post onset. By contrast all severe cases still tested positive at or beyond day 10 post onsets (Liu et al, the Lancet Inf. Des., 19 March 2020).

Peak viral load occurred 5-6 days after symptom onset. According to a report in the Lancet, April 2020, sputum has a higher viral load than the throat or nasal swabs. The median duration of RNA SARS-CoV-2 viral shedding is 12 days in the nasopharygnx and 19 days in the sputum.    

What is the median time for sero-conversion?

According to the World Health Organization (WHO), sero-conversion is the transition from a condition when no antibodies are present – seronegative, to a condition where antibodies are presented – seropositive. Median time of conversion is approximately 14 days. The presence of antibodies is less than 40% within the first week after onset of infection and then increases to 100% 15 days after the onset of infection. Sero-conversion occurred after 7 days in 50% of patients and 14 days in all patients, but was not followed by a rapid decline in viral load.

How long do infected people stay contagious?

As the amount of virus in the body reduces over time, the question is asked how long someone stays infected. This is still being studied, since the presence of the virus doesn’t necessarily mean they are able to infect other people.

Can coronavirus “reactivate” in cured patients?

According to Korean Center of Disease and Control (CDC) coronavirus may reactivate in cured patient. In a study of 51 patients said to have been cured in South Korea the patients tested positive again. “Rather than being infected again the virus may have been reactivated in these people, given they tested positive again shortly after being released from quarantine,” said the director general of the Korean CDC.

“While we are putting more weight on reactivation as the possible cause, we are conducting a comprehensive study at this point,” the director said. There have been many cases when a patient during treatment will test negative one day and positive another. A patient is deemed fully recovered when two tests conducted within a 24 hour interval show negative results.

Fear of re-infection in recovered patients is also growing in China, where the virus first emerged last December, after reports that some tested positive again and even died from the disease – after supposedly recovering and leaving hospital. There is little understanding why this is happening although some believe that the problem may lie in inconsistencies in test results.

In the future we will need to know how many adults without a confirmed history of infection of SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19), have antibodies to the coronavirus. In order to determine this critical information (data) for epidemiological models we need to conduct sero-survey. We need to analyze blood samples for two types of antibodies, IgM and IgG using an Enzyme Linked Immunosorbent Assay (ELISA) against SARS-CoV-2. This will help to determine the extent to which persons have encountered the novel coronavirus and identify the communities most affected in Antigua and Barbuda. We need data as we plan for the future.

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