Differential follow-up patterns in COVID-19 and comparison cohorts – Authors' reply
Authors: Maxime Taquet, Sierra Luciano, John R Geddes, Paul J Harrison
Journal: The Lancet Psychiatry (2021)

We thank Rebecca Fuhrer and James Hanley for their comments. They are correct that the timing of COVID-19 and the control events differ (as shown in the appendix of the Article),1Taquet M Luciano S Geddes JR Harrison PJ Bidirectional associations between COVID-19 and psychiatric disorder: retrospective cohort studies of 62 354 COVID-19 cases in the USA.Lancet Psychiatry. 2021; 8: 130-140Summary Full Text Full Text PDF PubMed Scopus (906) Google Scholar and that, in turn, the duration of available follow-up differs between cohorts. They are also right that, as a result, there is a possible risk that the matching between cohorts might be partly lost at follow-up. This loss of matching would occur, for instance, if patients who were diagnosed with COVID-19 in July, 2020, (ie, with less opportunity for follow-up) were systematically different in their baseline characteristics from patients who were diagnosed in March, 2020 (ie, with more opportunity for follow-up). Addressing this issue was the purpose of our sensitivity analysis, wherein cohorts were limited to people with a subsequent health visit within the 14 to 90 day period after diagnosis (as shown in the appendix of the Article).1Taquet M Luciano S Geddes JR Harrison PJ Bidirectional associations between COVID-19 and psychiatric disorder: retrospective cohort studies of 62 354 COVID-19 cases in the USA.Lancet Psychiatry. 2021; 8: 130-140Summary Full Text Full Text PDF PubMed Scopus (906) Google Scholar With the benefits of the longer follow-up that is now available compared with when we did the study, we ran an additional sensitivity analysis in which the same cohorts of patients (ie, with COVID-19 and influenza) as in our primary analysis were followed up until Feb 12, 2021. This analysis allowed us to distinguish people who were potentially lost to follow up in the 3 months after their diagnosis from people who had not yet made contact with a health-care organisation from the network. In this additional analysis, there was substantially less difference in the follow-up rates between cohorts, particularly at 15 days, where the number of people who were at risk of psychiatric illness differed only by 0·2% (ie, 62·2% of the COVID-19 cohort vs 62·0% of the influenza cohort). In this analysis, at 90 days, the relative risk of having had a psychiatric illness in the COVID-19 versus influenza cohorts was 1·86 (95% CI 1·65–2·06), which is similar to that in the primary analysis. This similarity provides further evidence that differences in loss of patients to follow-up do not account for the observed differences in rates of psychiatric diagnoses. Regarding the exclusion of patients from the analysis who had died after the index event, we included these patients as part of a sensitivity analysis in a follow-up study.2Taquet M, Geddes JR, Husain M, Luciano S, Harrison PJ. Six-month neurological and psychiatric outcomes in 236 379 survivors of COVID-19: retrospective cohort studies using electronic health records. Lancet Psychiatry (in press).Google Scholar Similar findings were obtained when patients who had died were included. SL is an employee of TriNetX. All other authors declare no competing interests. MT and PJH accessed and verified the data in the study and the corresponding author had final responsibility for the decision to submit for publication. Bidirectional associations between COVID-19 and psychiatric disorder: retrospective cohort studies of 62 354 COVID-19 cases in the USASurvivors of COVID-19 appear to be at increased risk of psychiatric sequelae, and a psychiatric diagnosis might be an independent risk factor for COVID-19. Although preliminary, our findings have implications for clinical services, and prospective cohort studies are warranted. Full-Text PDF Open AccessDifferential follow-up patterns in COVID-19 and comparison cohortsMaxime Taquet and colleagues1 showed that the incidence of a first psychiatric diagnosis in the 14–90 days after a diagnosis of COVID-19 was considerably higher than the incidence in the six matched comparison cohorts (ie, with influenza, other respiratory tract infections, skin infection, cholelithiasis, urolithiasis, and fracture of a large bone). To investigate possible explanations for these findings, we reconstructed the daily numbers of new diagnoses and patients at risk of psychiatric diagnosis in each cohort. Full-Text PDF