Serotype distribution among adults with community-acquired pneumococcal pneumonia in Japan between 2019 and 2022: A multicenter observational study

Abstract

Streptococcus pneumoniae is a leading cause of community-acquired pneumonia (CAP) in adults. With the introduction of pneumococcal conjugate vaccines (PCVs) into pediatric national immunization programs, the serotype distribution of pneumococcal disease among adults has changed due to indirect effect. In Japan, PCV15 and PCV20 have been introduced, and PCV21 is under review for approval in adults. This multicenter observational study assessed pneumococcal serotypes in 583 adult patients with community-acquired, culture-positive pneumococcal pneumonia from May 2019 to December 2022. Pneumococcal isolates were serotyped using the Quellung reaction. The median patient age was 74 years (interquartile range: 66-82 years), 383 (65.7%) patients were male, 387 (66.4%) patients had one or more underlying medical conditions, 425 patients (72.9%) were hospitalized, and 305 (52.3%) had a CURB-65 score ≥2. The most common serotypes were serotype 3 (12.5%), 35B (12.0%), 15A (7.7%), 11A (6.7%), and 23A (6.3%). The proportion of serotypes covered by PCV13, PCV15, PCV20, PPSV23, and PCV21 were 24.0, 28.0, 43.7, 44.1, and 71.9%, respectively. The proportions of vaccine-covered serotypes were similar between patients aged <65 and ≥65 years. Serotype 3 was more prevalent among patients living in nursing homes (25.9%) compared with those living at home (11.2%). The proportions of PCV20- and PCV21-covered serotypes suggest that these new vaccines may offer additional protection against adult pneumococcal pneumonia. Given the availability of newly developed PCVs for adults in Japan, reassessing the optimal pneumococcal vaccination policy for adults is warranted.

Keywords: Japan; Pneumococcal pneumonia; adult; nursing home; pneumococcal conjugate vaccines; serotype distribution.

Figure 1.

Pneumococcal serotypes detected in adult pneumococcal pneumonia patients. Bars represent the percentage of detected pneumococcal serotypes. (a) Pneumococcal serotypes detected in adult patients aged ≥18 years. (b) Pneumococcal serotypes detected in adult patients aged 18–64 years. (c) Pneumococcal serotypes detected in adult patients aged ≥65 years. Serotype 1, 5, 9 V, and 18C (included in PCV13), and serotype 2, 9N, 8 and 17F (included in PPSV23) were not detected.

Figure 2.

Pneumococcal serotypes detected in adult invasive and noninvasive pneumococcal pneumonia. Orange bars represent the percentage of detected pneumococcal serotypes in invasive pneumococcal pneumonia episodes, while green bars represent that in noninvasive pneumococcal pneumonia episodes. Invasive pneumococcal pneumonia was defined when isolation of streptococcus pneumonia came from blood or pleural effusion while noninvasive pneumococcal pneumonia was defined when isolation came from only sputum. Serotype 1, 5, 9 V, and 18C (included in PCV13), and serotype 2, 9N, 8 and 17F (included in PPSV23) were not detected.

Figure 3.

Percentage of adult pneumococcal pneumonia patients with serotypes included in PCV13, PCV15, PCV20, PPSV23, and PCV21, overall and by age group. Bars represent the percentage of pneumococcal pneumonia patients with pneumococcal serotypes included in each vaccine. PCV13 serotype include serotype 4, 6 B, 9 V, 14, 18C, 19F, 23F, 1, 5, 7F, 3, 6A, and 19A; PCV15 serotype include PCV13 serotype plus serotype 22F and 33F; PCV20 serotype include PCV15 serotype plus serotype 8, 10A, 11A, 12F, and 15 B; PPSV23 serotype include serotype 1, 2, 3, 4, 5, 6 B, 7F, 8, 9N, 9 V, 10A, 11A, 12F, 14, 15 B, 17F, 18C, 19A, 19F, 20, 22F, 23F, and 33F. PCV21 serotype include serotype 3, 6A, 7F, 19A, 22F, 33F, 8, 10A, 11A, 12F, 9N, 17F, 20, 15A, 15C, 16F, 23A, 23B, 24F, 31, and 35B.

Figure 4.

Percentage of adult pneumococcal pneumonia patients with serotypes included in PCV13, PCV15, PCV20, PPSV23, and PCV21, in invasive and noninvasive pneumococcal pneumonia episodes. Bars represent the percentage of pneumococcal pneumonia patients with pneumococcal serotypes included in each vaccine. PCV13 serotype include serotype 4, 6 B, 9 V, 14, 18C, 19F, 23F, 1, 5, 7F, 3, 6A, and 19A; PCV15 serotype include PCV13 serotype plus serotype 22F and 33F; PCV20 serotype include PCV15 serotype plus serotype 8, 10A, 11A, 12F, and 15 B; PPSV23 serotype include serotype 1, 2, 3, 4, 5, 6 B, 7F, 8, 9N, 9 V, 10A, 11A, 12F, 14, 15 B, 17F, 18C, 19A, 19F, 20, 22F, 23F, and 33F. PCV21 serotype include serotype 3, 6A, 7F, 19A, 22F, 33F, 8, 10A, 11A, 12F, 9N, 17F, 20, 15A, 15C, 16F, 23A, 23B, 24F, 31, and 35B. Invasive pneumococcal pneumonia was defined when isolation of streptococcus pneumonia came from blood or pleural effusion while noninvasive pneumococcal pneumonia was defined when isolation came from only sputum.

Figure 5.

Pneumococcal serotypes detected in adult pneumococcal pneumonia patients living at home and those living in nursing homes. Orange bars represent the percentage of detected pneumococcal serotypes in patients living at home, while green bars represent that in patients living in nursing homes. Serotype 1, 5, 9 V, and 18C (included in PCV13), and serotype 2, 9N, 8 and 17F (included in PPSV23) were not detected.

Figure 6.

Percentage of adult pneumococcal pneumonia patients with serotype 3 and vaccine-covered serotypes, overall, in patients living at home, and in patients living in nursing homes.