So What Are The Risk Factors and Identifying Demographics for Testing Positive to SARS-CoV-2? 

A study published in the Lancet Infectious Diseases by the Oxford Royal College of General Practitioners Research and Surveillance Centre looked at patients who were tested for Coronavirus between January and April 2020.  This was one of the first and largest cross-sectional analyses using primary care data to assess risk factors for testing positive for SARS-CoV-2. 

They found increasing age, male sex, increasing deprivation, urban location, and black ethnicity were associated with increased odds of a positive SARS-CoV-2 test. 

Interestingly, current smoking was linked with decreased odds of a positive test. 

Chronic kidney disease and increased BMI, as in overweight, were the only clinical factors independently associated with a positive test.

Literature review suggests that COVID-19 has affected more men than women and principally those aged 30 to 65 years with around half of the cases being older than 50 years.  In their study they found a similar increased risk of positive SARS-CoV-2 test in men and also in a population older than 40 years old.

SARS-CoV-2 viral transmission is known to be associated with high population density due to increased social mixing which was consistent with their study which found higher odds of a positive test in urban areas. 

Social deprivation has been associated with an increased risk of other respiratory infections and there is evidence that the risk of COVID-19 related death is higher in more deprived areas of England, although this analysis has not been adjusted for any other potential confounding variables. 

This study found an association between increasing deprivation and increased odds of a positive test, independent of household size, urban location and smoking. 

Interestingly, they did not find an association between increased household size and risk of SARS-CoV-2 positivity despite there being previously reported high risk of transmission among household contacts.  (Behavioural responses to social distancing measures might have accounted for this finding).  Possibly small households may only have a studio flat or a single room occupancy without communal space and people living in such might be more inclined to risk infection by leaving home.

Previous evidence has raised concern about the potential increased risk of adverse COVID-19 outcomes amongst racial groups such Asians and Black ethnicity, but there have been few studies which have assessed risk by ethnic group.  An analysis of 3,370 people admitted to intensive care in the UK with confirmed COVID-19 found that 402, that is 11.9% were of Black origin, 486, that is 14.4% were Asian and 2236, that is 66.4% were of White origin, compared with respective national figures of 3.3%, 7.5% and 86%. 

However, these results did not adjust for potential sociodemographic or clinical variables.  In this Oxford study the overall numbers of black, Asian and people from minority ethnic racial groups were small which would suggest that the results should be interpreted with caution. 

However, they did find that people of black origin had higher odds of a positive SARS-CoV-2 test result than white people which remains significant after adjusting for other comorbidities such as hypertension and diabetes which in themselves are increased in a black ethnic group. 

Other socioeconomic factors which were not measured such as employment in high risk positions, education, income, barrier to healthcare, which might have contributed to this association should be urgently explored. 

Previous reviews have shown that people with COVID-19 who have chronic comorbidities such as hypertension, diabetes, and cardiovascular disease are at a higher risk of progressing to severe COVID-19 disease.  This study found no evidence of an association between these conditions and a positive SARS-CoV-2 test.  However, chronic kidney disease and obesity were associated with testing positive for SARS-CoV-2 and these conditions themselves are associated with an increased risk of other respiratory infections.

Previous studies have reported that smoking is associated with an increased risk of intensive care unit admission or death among patients with COVID-19.  However, some studies have reported a lower prevalence of smoking among people with COVID-19.  However, this study found that active smoking was associated with lower odds of having a positive test result – this might be accounted for by the fact that active smoking might affect the nasopharyngeal viral load and therefore affect RT-PCR test sensitivity, rather than protecting against actual infection, although this effect is not known to occur with influenza testing. 

Alternatively, as patients with symptoms are more likely to have been tested and included in their analysis, selection bias might have affected this result.  Smokers are more likely to have a cough and are therefore more likely to be tested for SARS-CoV-2 than non-smokers even when they are SARS-CoV-2 negative – this would mean that more frequent testing could increase the proportion of smokers with a negative SARS-CoV-2 result which would clearly bias the result. 

Interestingly though, ex-smokers and people with known chronic obstructive airway disease would be expected to cough more also, but these groups did not show higher odds of a SARS-CoV-2 positivity.  It is postulated that nicotine might down regulate the angiotensin-converting enzyme 2 receptors which are used by SARS-CoV-2 for cell entry, although studies have found increased angiotensin-converting enzyme 2 lung expression among smokers and people with chronic obstructive pulmonary disease. 

The authors of the study conclude that it should not be considered that smoking prevents SARS-CoV-2 infection and it should not be encouraged for people to continue smoking.  The study concludes that increasing age, male sex, socioeconomic deprivation, increased population density, black ethnicity, chronic kidney disease and obesity are all associated with an increased risk of a positive SARS-CoV-2 test.  The findings with smoking need to be studied more extensively. 

The London General Practice prides itself on its ability to keep abreast on all aspects of COVID-19 infection which affect general practice and its patients. 

During this difficult time The Practice has maintained its clinical governance structure and holds regular audit and doctor meetings via video conferencing three times a week in order for all of its practitioners to be kept abreast of all current developments within this pandemic and to continue to monitor all other aspects of diseases which may have been side stepped during this difficult time.

The Practice is still undertaking face-to-face consultations and home visits for those with no acute florid COVID symptoms wearing full PPE and is able to look after those with acute conditions and those whose chronic conditions require maintenance.

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