Association of pre-pandemic respiratory system diseases with long COVID: a population-based case-control study

Long COVID, defined as diverse symptoms persisting > 3 months post-infection, remains a major post-pandemic healthcare burden. Here we investigate risk factor posed by pre-existing respiratory symptoms and illnesses for development of long COVID, with focus on individuals with mild-to-moderate COVID-19 at the primary infection, that did not require hospitalization during the primary SARS-CoV-2 infection. This case-control study was designed to investigate the prevalence of respiratory system-related diagnoses in adult; non-hospitalized long COVID patients (cases) compared to matched controls without a history of long COVID. Data was extracted from the Stockholm Region’s database (VAL) and included diagnoses 12 months pre- and 6 months post-long COVID diagnosis as well as pre-pandemic diagnoses (year 2019). Conditional logistic regression models were applied. Patients with Long COVID displayed higher frequencies of pre-pandemic respiratory conditions (year 2019) as well as 12 months before long COVID diagnosis compared to controls, including acute upper respiratory tract infections (men: Odds ratio (OR) 2.47, women: OR 2.22), asthma (men: OR 1.76, women: OR 1.95), and bronchitis (men: OR 2.15, women: OR 2.71). ORs for asthma were the highest 12 months before long COVID diagnosis (men: OR 4.18, women: OR 3.76). Patients with Long COVID with a mild-to-moderate primary SARS-CoV-2 infection had higher prevalence of pre-existing respiratory conditions than controls, suggesting that respiratory diseases including asthma were a significant risk factor for long COVID also in the non-hospitalized population. Understanding the link between common respiratory conditions managed in primary care, including asthma and bronchitis, and long COVID is vital for refining clinical strategies and improving outcomes in post-viral conditions. Pre-pandemic respiratory diagnoses, including asthma, were more common among individuals later diagnosed with long COVID compared with matched controls. In line with previous literature, most long COVID cases in our cohort were female.