Epidemiology of human parainfluenza virus type 3 (HPIV-3) and respiratory syncytial virus (RSV) infections in the time of COVID-19: findings from a household cohort in Maryland


 
 
 During the COVID-19 pandemic, human parainfluenza type 3 (HPIV-3) and respiratory syncytial virus (RSV) circulation increased as non-pharmaceutical interventions were relaxed. Using data from 175 households (n = 690 members) followed between November 2020–October 2021, we characterized
 HPIV-3 and RSV burden in children aged 0-4 years and infection patterns in their households.
 
 
 
 Households with ≥1 child aged 0-4 years were enrolled and members collected weekly nasal swabs (NS) and additional swabs with COVID-like illness onset. We tested all NS from symptomatic episodes in children aged 0-4 years for HPIV-3, RSV, and SARS-CoV-2 by reverse-transcriptase polymerase chain reaction (RT-PCR). Among children with HPIV-3 or RSV infection, we tested all contemporaneous NS collected from household members. We compared incidence rates (IRs) of symptomatic infection with each virus among children aged 0-4 years during epidemic periods, identified household primary infections as the earliest detected infection, and examined community exposures associated with primary infection.
 
 
 
 Overall, 41/175 (23.4%) households had individuals with HPIV-3 (n = 45) or RSV (n = 46) infections. Among children aged 0-4 years, IRs of symptomatic infection/1,000 person-weeks were 8.7[6.0, 12.2] for HPIV-3, 7.6[4.8, 11.4] for RSV, and 1.9[1.0, 3.5] for SARS-CoV-2. 35/36 primary HPIV-3 or RSV infections occurred in children aged 0-4 years. Children with childcare/preschool attendance had higher odds of primary infection (OR = 10.81, 95% CI: 3.14-37.23).
 
 
 
 Among children aged 0-4 years in this cohort, IRs of symptomatic HPIV-3 and RSV infection were four-fold higher than for SARS-CoV-2 during epidemic periods. HPIV-3 and RSV were almost exclusively introduced into households by infants and preschool children.
