The risk factors for severe coronavirus disease 2019 (COVID-19) have been established on the basis of observational studies. However, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to cause thousands of COVID-19 cases all over the world, and the risk factors are unclear. A new study released on the medRxiv* preprint server deals with this aspect of the pandemic.
Risk of severe COVID-19
Severe COVID-19 is more likely for male patients, those of Black or Asian ethnicity, obesity, those of low socioeconomic status, and those with underlying diseases such as diabetes, cardiovascular disease, chronic obstructive pulmonary disease (COPD) and hypertension.
However, the risk of contracting the infection itself may be distinct from that of developing severe disease. An earlier UK study reports a higher risk of infection in younger adults relative to older individuals, and seropositivity studies support this conclusion.
Self-protective behavior and lower infection risk
On the other hand, the occurrence of comorbid conditions is linked to a lower risk of infection. This is possibly due to protective behavioral changes adopted by such individuals, such as keeping away from public places and avoiding social contacts.
This possibility has not been investigated, however, and it remains a plausible hypothesis. Nonetheless, the current study also seeks to examine the role of occupational and socioeconomic factors, and lifestyle-related factors such as diet and the use of supplements.
The study, entitled COVIDENCE UK, was designed to follow up infected individuals throughout their clinical course to uncover such risk factors.
Data was collected via a baseline questionnaire on COVID-19-like symptoms, test results, and the presence of risk factors. This was followed by monthly questionnaires to detect new cases as well as potential symptoms, and the study period extended from May 1, 2020, to February 5, 2021.
There were over 17,000 participants up to November 2, 2020, of which those who probably were COVID-19 positive, in the form of a positive test and/or probable symptoms. Of the roughly 15,000 participants left, the mean age was 59 years, and 70% were female, while the overwhelming majority (95%) were White.
Over the 2.6 million person-days of the study, there were 446 participants who had one or more positive tests for the virus. Of these, 32 required hospitalization.
What were the results?
The first pass threw up risk factors for COVID-19, such as Asian ethnicity, social housing status and being a frontline worker. People who lived in overcrowded housing, or had visitors from outside their household the previous week, were also at higher risk for infection.
Similar was the case with those living with children or working-age adults, having a dog, having commuted to work in the previous week, and paying more visits to indoor public places, including stores, per week. Being overweight or obese, having had BCG vaccination previously, being a drinker, and sleeping too much or too little every night, was also associated with a higher risk of infection.
Those at lower risk were adults below 60 years, better educated and wealthier, being shielded, and engaging in low-impact activities regularly. Those with a history of asthma and atopic disease, or who were on immunosuppressants, inhaled corticosteroids or bronchodilators, or were in the fourth quartile for fruit and vegetable intake, or were on vitamin D supplements.
However, the number of working-age adults in a household was closely related to being a multi-generational household, and being overcrowded at home. Thus, the last was used, and the others were excluded from the final analysis.
In this final model, the risk factors for SARS-CoV-2 infection were of Asian origin, these individuals being at twice the risk; living in overcrowded households, where every additional one person per two bedrooms meant 25% increased risk, while being a frontline worker pushed up the risk by 50%.
Heavy people also had higher infection risk, at 50% and 38% more for overweight and obese individuals.
People with atopy had 25% lower risk, while those on systemic immunosuppressive drugs had only half the risk of COVID-19, compared to the general population. Atopic asthma shared in the decreased risk, by 35%, but not non-atopic asthma.
If the diagnosis of probable COVID-19 was based on symptoms, the risk of being positive for the infection was higher among Asian-origin individuals, those living in rented and overcrowded homes, and frontline workers in non-health/social work jobs.
Those on cod liver oil or those taking selective serotonin reuptake inhibitors, with lower self-reported health, also had a higher risk of infection, compared to the lower risk found in those aged 50 years or above.
What are the implications?
The study strongly suggests that overcrowding at home and frequent visits to shops or other public places are causes for increased viral transmission, in a dose-dependent manner. Being of Asian origin, mixing with non-household others more often, and being a frontline worker, as well as having a heavier body, were also independent predictors of higher risk.
These findings are not new, supporting the reports of higher susceptibility to the virus as well as more severe disease once infected, among those of Asian origin, quite independent of other factors like overcrowding at home, or occupation. These ethnic underpinnings of risk need to be understood as soon as possible.
The presence of high BMI as a risk factor is also not new, and has been linked to a state of immune dysregulation that predisposes to infection and to severe COVID-19.
Interestingly, the presence of comorbidities was not linked to a higher risk of disease, neither was male sex or advancing age. Atopy was linked to a lower risk of infection, possibly because of the lower expression of angiotensin-converting enzyme 2 (ACE2), which is the receptor for the virus on the host cells.
This study had a very high participation rate, strengthening its findings. Moreover, the monthly follow-up allowed for the identification of mild infections and temporally associated potential risk factors, unlike earlier studies.
Our finding that visits to other households and indoor public places were associated with increased risk of disease supports the case for restricting such activities as a public health strategy to control disease.”
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.