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18th January 2021
Since March 2020, members of the public in the UK have been able to download and register with a smartphone app as part of an ongoing COVID-19 symptom study. Individuals who register with the app self-report demographic and healthcare data (i.e., co-morbidities) as well as any COVID-19-related symptoms. The app has been downloaded by over 2.4 million people and for the present analysis, researchers collected COVID-19-related symptom data between March and April 2020. Participants were asked to report if they felt ‘physically normal’ and those answering no were invited by the app to record the presence of 14 symptoms that have been associated with COVID-19. The main outcome for the study was the development of ‘classic’ symptoms of COVID-19, i.e., fever, new persistent cough and breathlessness and the association of this symptom triad with current smoking status. They also explored the relationship between smoking, a positive PCR test result and hospital attendance.
During the study period there were 2,401,982 registered users (63.3% female) with a mean age of 43.6 years, of whom, 834,437 (35%) reported not feeling ‘physically normal’. The team then classified all registered participants into one of four groups; those who had tested positive for COVID-19, (SC2P); those who tested negative (SC2N); those self-reporting COVID-19 symptoms and who thus believed they had the virus (SC2S); the remainder who made up a group termed ‘standard users’. Among standard users, current smokers were more likely to report developing the COVID-19 triad symptoms, suggesting a diagnosis of infection (odds ratio, OR = 1.14, 95% CI 1.10 – 1.18, p < 0.001) and to report a higher symptom burden (defined as reporting > 5 of the 14 symptoms), than non-smokers. Smoking was also associated with a higher symptom burden in both the SC2S and SC2P groups. Interestingly, while smoking rates were lower among those testing positive for the virus, i.e., in the SC2P group (thus suggesting a protective effect against the virus from smoking), their reported symptom burden was higher than non-smokers. Furthermore, smokers in the SCP2 group had a higher risk of attending hospital due to COVID-19 compared to non-smokers (OR = 2.11 95% CI 1.41 – 3.11, p < 0.001) and this association remained even after adjusting for co-morbidities (OR = 1.87).
Summarising these findings, the authors made the following observations. Smoking was associated with an increased risk of developing self-reported COVID-19 symptoms and a greater symptom burden. A higher symptom burden was also evident among smokers testing positive for the virus and that these individuals were more likely to visit hospital because of their symptoms.
The authors concluded by calling for smoking cessation to be a part of public health campaigns during the current pandemic.
Hopkinson NS et al. Current smoking and COVID-19 risk: results form a population symptom app in over 2.4 million people. Thorax 2021