Abstract
BACKGROUND: Current evidence suggests that in young children with community-acquired alveolar pneumonia (CAAP), bacterial-viral coinfections (mostly respiratory syncytial virus [RSV]-pneumococcus coinfections) are more prevalent among hospitalized children than among outpatients and that RSV-pneumococcal coinfections are more frequently associated with non-PCV13 serotypes. Based on this background, we speculated that following pneumococcal conjugate vaccine [PCV] implementation, the decline of hospitalized CAAP episodes would be lower than that of outpatient episodes. METHODS: This analysis was a part of an ongoing (since 2004) population-based, active surveillance in children < 5 years, including all CAAP visits to the pediatric emergency room in southern Israel. Community-acquired alveolar pneumonia was radiologically confirmed by consensus reading. Episodes were divided into hospitalized and those discharged without hospitalization (outpatients). We used a negative binomial regression model to evaluate PCV7/PCV13 impact by age and ethnic group using monthly and yearly incidence rates. Analyzed periods were pre-PCV (2004-2009), PCV7/PCV13 transition (2009-2011), early-PCV13 (2011-2015), and late-PCV13 (2015-2019). RESULTS: Of 11 130 episodes, 3677 and 7633 were outpatients and hospitalized, respectively. Post-PCV incidence dynamics significantly diverged between the 2 study groups. (1) During the PCV7/PCV13 transition, outpatient rates significantly declined, but not those of hospitalizations. 2) During late-PCV13 period, a significantly greater decline was reached among outpatients (67%; 95% confidence interval [CI] 62%-71%) versus hospitalized (47%; 95% CI 41%-54%). This difference remained for all age and ethnic groups. CONCLUSIONS: The marked divergence in PCV impact between hospitalized and outpatient episodes is intriguing, but consistent with previous studies suggesting that hospitalized CAAP was associated with a lower proportion of PCV13 serotypes, in conjunction with viral-bacterial (mostly RSV-pneumococcus) coinfections.