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.