People living in the most deprived areas of Britain are more than four times likelier to test positive for COVID-19 than those living in the richest neighbourhoods, new research showed Saturday.

A University of Oxford study looked at more than 3,600 COVID-19 test results from national programmes and found that deprivation, age and chronic liver disease all increased the likelihood of testing positive.

Of that sample, the more than 660 people living in the most deprived areas, 29.5 percent tested positive, compared with just 7.7 percent of those in richer areas, the study showed. Those aged 40-64 were at the highest risk, with 18.5 percent of that age group testing positive compared to just 4.6 percent of under 17s.

A greater percentage of men (18.4 percent) tested positive than women (13.3 percent). And people of black ethnicity were more than four times likelier to test positive than those of white ethnicity -- 62.1 percent vs 15.5 percent.

The authors, however, cautioned that the cohort of black people tested in the study was small -- only 58 people.

"With each day that passes our knowledge of COVID-19 improves," said Gayatri Amirthalingam, from Public Health England and co-author of the study printed in The Lancet. "This analysis of primary care outcomes of individuals testing positive for virus is an important contribution to our wider understanding of how COVID-19 is affecting people of different demographic groups."

The study has a number of limitations as it relies only on test results from routine testing programmes, which may skew the demographics of people included in the research. Nevertheless, lower income appeared to be a significant COVID-19 risk factor.

"We found an association between increasing deprivation and increased odds of a positive test, independent of household size, urban location, and smoking," the authors said.

'Existing inequalities'

The results showed current smokers were in fact less likely to test positive than non-smokers (11.4 percent vs 17.9 percent). But that does not mean smoking protects an individual from COVID-19.

For one thing, smokers are more likely to cough -- a key symptom of the novel coronavirus -- and therefore may be more likely to get tested even when not sick. It is also possible that smoking affects the efficacy of current COVID-19 swab tests.

"As well as the well-documented harms to overall health from smoking, there is potential for smoking to increase the severity of COVID-19 disease," said Simon de Lusignan, director of the Royal College of GPs Surveillance Centre.

Writing in a linked comment article, Rachel Jordan, a researcher from the University of Birmingham, said the study could help shape testing programmes by prioritising at-risk communities. "What is fundamentally clear is that whatever the specific risk factors, the COVID-19 pandemic exacerbates existing socioeconomic inequalities," said Jordan, who was not involved in the research.