Pneumococcal Carriage and Disease in Adults in England, 2011–2019: The Importance of Adults as a Reservoir for Pneumococcus in Communities

Abstract

Background. Pneumococcal carriage in healthy adults and its relationship to invasive pneumococcal disease (IPD) is not well understood. Methods. Nasal wash samples from adults without close contact with young children (Liverpool, UK), 2011–2019, were cultured, and culture-negative samples tested by polymerase chain reaction (PCR). Pneumococcal carriage in adults 18–44 years was compared with carriage among pneumococcal conjugate vaccine–vaccinated children aged 13–48 months (nasopharyngeal swabs, Thames Valley, UK) and national IPD data, 2014–2019. Age group–specific serotype invasiveness was calculated and used with national IPD data to estimate carriage serotype distributions for ≥65 years. Results. Overall, 98 isolates (97 carriers) were identified (3 solely by PCR) from 1631 ≥18 years adults (standardized carriage prevalence 6.4%). Despite different carriage and IPD serotype distributions between adults and children, serotype invasiveness was highly correlated (R = 0.9). Serotypes 3, 37, and 8 represented a higher proportion of adult carriage than expected. Predicted carriage serotype distributions for ≥65 years aligned closest with the young adult carriage serotype distribution. Conclusions. Nasal wash technique is highly sensitive. For some serotypes carried by adults aged ≥65 years, other adults may be an important reservoir for transmission. Age groups such as older children should also be considered.