Pleural fluid nucleic acid testing enhances pneumococcal surveillance in children

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Background and objective:National surveillance of invasive pneumococcal disease (IPD) includes serotypingStreptococcus pneumoniae(SP) isolates from sterile site cultures. PCR is more sensitive and can identify more SP serotypes (STs) in culture-negative samples. The aim of this study was to determine whether enhanced surveillance of childhood empyema, using PCR, provides additional serotype information compared with conventional surveillance.Methods:Pleural fluid (PF) from children with empyema were cultured and tested by PCR to identify SP, targeting the autolysin gene (lytA). Multiplex PCR-based reverse line blot assay was used to identify SP STs. Corresponding IPD surveillance and serotype data were obtained from the National Notifiable Diseases Surveillance System (NNDSS).Results:Eighty-nine children with empyema, aged ≤16 years, were recruited between April 2008 and March 2009, inclusive. SP was isolated from 5/84 (5.9%) PF cultures and by PCR in 43/79 (54.4%) PF samples. Serotypes were unidentifiable in 15 samples. The frequency of six serotypes (or serotype pairs) identified in 28 samples, including one with two serotypes, were: ST1,n= 4/29 (13.8%); ST3,n= 9/29 (31.0%); ST19A,n= 12/29 (41.4%); ST7F/7A,n= 1/29 (3.4%); ST9V/9A,n= 1/29 (3.4%); ST22F/22A,n= 2/29 (6.9%). Over the same period, 361 IPD patients, aged 16 years or less, were notified to NNDSS. Among 331 serotypeable NNDSS isolates (71.5% from blood), the frequencies of ST1 and 3 were significantly lower than in PF samples: ST1,n= 8/331 (2.4%;P< 0.05); ST3,n= 13/331 (3.9%;P< 0.0001).Conclusions:The use of PCR to identify and serotype SP in culture-negative specimens provides additive information.

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