Vol.59 No.6 November 2011
Current status of invasive pneumococcal diseases and the preventive pneumococcal vaccines in Japan
Laboratory of Molecular Epidemiology for Infectious Agents, Kitasato Institute for Life Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo, Japan
Abstract
Streptococcus pneumoniae induce invasive pneumococcal diseases(IPD) that may cause serious sequelae or be fatal, even in these days when effective antibacterial therapies are available. This article discusses the current status of IPD in Japan as well as capsular typing involved in the prediction of vaccination efficacy, primarily based on the results of an epidemiological survey conducted in 2006. The age groups that were most frequently affected by IPD were infants aged ≤1 year, and adults aged ≥50 years. In contrast to sepsis and bacteremia which were common among children, severe pneumonia was predominant among adults. Patients with underlying conditions were at a high risk for death or neurological sequelae (P=0.04 for children and P<0.01 for adults). Statistical analysis revealed that a white blood cell count of ≤5.0×109 cells/L and a platelet count of ≤130×109 cells/L on hematology tests immediately after hospital admission were highly predictive of a poor prognosis.
In Japan, voluntary vaccination with pneumococcal conjugate vaccine(PCV7) for children was licensed in 2010, and the coverage for IPD was 75%. Pneumococcal polysaccharide vaccine(PPV23) covered 85% of adult IPD cases. The capsular types of strains isolated from children and from adults were obviously different. Specifically, serotypes 6B, 19F, 14, and 23F, which are common among gPRSP strains, were predominant in isolates from children, while serotypes 12F, 3, 6B, and 14, which are common among gPISP strains, accounted for the majority of isolates from adults. Among these isolates, the serotype 12F strain from adults was subjected to pulsed field gel electrophoresis, which showed an identical DNA profile among strains with the same genotype. This finding suggests that strains with a new capsular type spread rapidly in a short time around Japan, a densely populated country. Analysis using multilocus sequence typing, which allows global comparison and sharing of epidemiological information on bacterial infections, suggested the occurrence of genetic recombination among capsular serotypes (capsular switching).
S. pneumoniae are evolving by changing themselves, as represented by (i) the emergence of highly pathogenic strains with new capsular serotypes, such as 6C and 11E; (ii) the emergence of highly resistant strains due to antibiotic pressure; and (iii) the emergence of strains with capsular switching caused by the global popularization of pneumococcal vaccines. It is concluded that global-scale epidemiological studies are needed in addition to vaccination, which is indispensable for the control of IPD.
Key word
Streptococcus pneumoniae, invasive pneumococcal disease, pneumococcal vaccine
Received
July 20, 2011
Accepted
July 27, 2011
Jpn. J. Chemother. 59 (6): 561-572, 2011
