To the Editor: Streptococcus pneumoniae is the main cause of community-acquired pneumonia (CAP) and a leading cause of mortality in older adults.1 Previous studies have reported the effectiveness of 23-valent pneumococcal polysaccharide vaccine (PPV23) against invasive pneumococcal disease (IPD) in older adults.2, 3 After the introduction of 7-valent pneumococcal conjugate vaccine (PCV7) for children, an indirect effect of PCV7 against IPD in older adults was identified, possibly mediated through a herd immunity effect of the decreased presence and circulation of the PCV7 serotypes.4-6 In contrast to bacteremic pneumococcal pneumonia, the clinical effectiveness of pneumococcal vaccines against nonbacteremic pneumococcal pneumonia remains unclear because of the absence of a sensitive tool to make an etiological diagnosis. PCV7 and PPV23 have been available in Taiwan since October 2005 and January 2001, respectively. This hospital-based surveillance of hospitalized patients with nonbacteremic pneumococcal CAP (NBPCAP) evaluated the effect of PCV7 and PPV23 vaccination in Taiwan. The study included patients treated at National Taiwan University Hospital, a 2,000-bed tertiary care hospital in Taiwan. A total of 134 hospitalized patients with NBPCAP, determined according to a positive S. pneumoniae urinary antigen test (Binax NOW S. pneumoniae urinary antigen test; Binax, Inc., ?, ME), were identified from databases of the microbiology laboratory from January 2004 to December 2008. NBPCAP was defined as a clinical diagnosis of CAP plus a positive S. pneumoniae urinary antigen test and negative blood culture results. Information on the number of doses of PPV23 and PCV7 distributed in Taiwan was obtained from the manufacturers: Merck Sharp & Dohme Corp. (Taipei, Taiwan) and Wyeth-Ayerst (Asia) Ltd. (Taipei, Taiwan), respectively. The mean incidence of NBPCAP during the study period was 4.0 cases per 10,000 hospitalizations, and a decline in incidence from 2004/05 (4.9 cases per 10,000 hospitalizations) to 2006/08 (3.5 cases per 10,000 hospitalizations) was noted (29.9% reduction, 95% confidence interval (CI), 0.3–59.3%; P=.048). The annual incidence according to age group is shown in Figure 1. From 2004/05 to 2006/08, there was no significant change in the combined incidence rates of patients younger than 5 (33.7 cases to 32.5 cases per 10,000 hospitalizations; 3.5% reduction; 95% CI=−42.3–49.4%; P=.97) or patients aged 5 to 64 (1.6–1.5 cases per 10,000 hospitalizations; 7.9% reduction; 95% CI=−59.8–75.6%; P=.96), whereas the reduction in patients aged 65 and older was significant (5.1–1.8 cases per 10,000 hospitalizations; 64.1% reduction, 95% CI=13.3–115.0%; P=.009). Annual incidence (cases per 10,000 hospitalizations) of nonbacteremic pneumococcal community-acquired pneumonia according to age group, 2004/08. The overall mortality rate was 6%, and all deaths occurred in patients aged 65 and older, in whom the mortality rate was 27.6%. In the univariate analysis, diabetes mellitus (odds ratio (OR)=10.2), solid organ cancer (OR=24.6), and immunosuppressive therapy (OR=12.0) were associated with fatal outcome (all P<.01). From 2004/05 to 2006/08, there was no significant change in mortality (4.8–6.9%; P=.72) and intensive care unit admission (35.5–36.1%; P=.92) rates, whereas hospital stays were shorter in 2006/08 (mean days ± standard deviation, 16.6 ± 15.0 to 12.3 ± 13.0; P=.02). After the introduction of PPV23 in 2001, the overall vaccination rate was less than 1% in Taiwan before 2007; the cumulative coverage rate in persons aged 75 and older reached 12% in 2007 and 41% in 2008. After the introduction of PCV7 in October 2005, the cumulative coverage rate in children younger than 5 was 0.7% in 2005, 8.6% in 2006, 15.9% in 2007, and 25.2% in 2008. This study found a significant decline in NBPCAP in hospitalized elderly patients after the introduction of PCV7 and greater usage of PPV23. Only a few studies have evaluated the effectiveness of PPV23 against nonbacteremic pneumococcal pneumonia, which has been estimated to be four times as frequent as bacteremic episodes.7 Two studies have shown that PPV23 does not provide significant protection against nonbacteremic pneumococcal pneumonia.8, 9 A more-recent case–control study showed that PPV23 was effective against nonbacteremic pneumococcal pneumonia (42% efficacy) in adults aged 50 and older.10 In the present study, the observed effect (64.1%) of partial PPV23 and PCV7 vaccination against NBPCAP in hospitalized elderly patients was superior to that in the previous study.10 Although it is unclear whether the herd effect of PCV7 would be similar in nonbacteremic cases and IPD, the results of the current study suggest a possible combined effect of PPV23 (direct) and PCV7 (indirect) against NBPCAP in older adults. Further studies are needed to elucidate the direct and indirect benefits of pneumococcal vaccinations against NBPCAP in older adults. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this paper. Author Contributions: Sheng-Hsiang Lin: study concept and design; acquisition, analysis, and interpretation of the data; and manuscript writing. Che-Kim Tan, Chih-Cheng Lai, and Cheng-Yi Wang: acquisition, analysis, and interpretation of the data. Po-Ren Hsueh: study concept and design, manuscript preparation. Sponsor's Role: None.
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Lin et al. (2010) studied this question.
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