Pneumococcal Invasive Disease in Infants Younger Than 60 Days in the United States in the 13-Valent Pneumococcal Conjugate Vaccine Era

Abstract

Background. The impact of PCV13 on invasive pneumococcal disease (IPD) in infants <60 days, who are too young to be immunized, is unknown. We compared the serotype (St) distribution, antibiotic susceptibility and clinical syndrome of infants <60 days with IPD 5 years before and 5 years after the introduction of PCV13. Methods. We identified infants <60 days with IPD at 8 children's hospitals in the US (1 January 2005-31 December 2015). Pneumococcal isolates were collected prospectively. Serotyping and antibiotic susceptibility were performed in a central laboratory. Patients were divided into 3 subgroups: pre-PCV13 (2005-2009), transitional year (2010) and post-PCV13 (2011-2015). Dichotomous variables were analyzed by χ2 test and continuous variables with non-parametric tests. Results. During the study period, 53 of 1816 (2.9%) children with IPD were infants <60 days; 27 of 1004 (2.7%) during 2005-2009 and 20 of 644 (3.1%) during 2011-2015 (p = 0.6). Four (7.5%) patients developed IPD within 24 hours of life, and 10 (18.9%) in the first 7 days. A total of 73.6% of cases occurred in infants aged 31-59 days. Four infants were born at <37 weeks. Bacteremia without focus was the most common clinical syndrome (43.4%), followed by meningitis (32.1%), mastoiditis (11.3%) and pneumonia (9.4%). The most common presentation among infants aged ≤7 days was meningitis (70%) and among infants aged >7 days was bacteremia (48.8%). The age distribution and clinical syndromes remained unchanged after the introduction of PCV13. Two term infants with meningitis died. Overall, the most common St was 19A (22.4%). St19A decreased from 29.6% in 2005-2009 to 17.6% in 2011-2015 (p = 0.5). PCV13 Sts caused 81.5% and 58.8% of cases before and after the introduction of PCV13 (p = 0.2), respectively. In 2011-2015, Sts 19A, 19F and 3 remained the most common Sts. St 7F was not identified in 2011-2015. Overall, 70% of isolates were penicillin susceptible (MIC ≤0.06). Penicillin susceptibility decreased from 85.2% in 2005- 2009 to 58.8% in 2011-2015 (p = 0.08). Conclusion. After the introduction of PCV13, the number of cases of IPD in infants <60 days slightly decreased. PCV13 serotypes 19A, 19F and 3 were the most common Sts affecting this age group in 2011-2015, which contributed to the penicillin nonsusceptibility increase. (Figure Presented) .