INTRODUCTION

1. Pneumococcal serotyping for surveillance of invasive pneumococcal diseases in Singapore, 2011 La My Van1, Siti Zulaina MS1, Ariel Chua2, Roland Jureen4, Nancy WS Tee3, Raymond Lin1,2 ______________________________________________________________________________________________ 1National Public Health Laboratory, 2Ministry of Health, 3KK Women’s & Children Hospital and 4National University Health System INTRODUCTION Infection due to Streptococcus pneumoniaehas played a significant role in morbidity and mortality among young children and elderly adults worldwide1. We report data from pneumococcusserotyping performed by the National Public Health Laboratory (NPHL) and the KK Women’s and Children Hospital (KKH) from January to December 2011 within the framework of the nationwide pneumococcus surveillance programme in Singapore. The aim of the programme is to serotype invasive pneumococcal isolates collected from the whole of Singapore and to monitor the serotype distribution of invasive pneumococcal disease (IPD) among Singapore population. (A) (B) METHOD Six public hospitals in Singapore sent Streptococcus pneumoniaeisolates from sterile site cultures, e.g. blood, cerebrospinal fluid (CSF), pleural and peritoneal fluid, to NPHL for serotyping. The microbiology laboratory at KKH serotyped their invasive pneumococcal isolates. Serotyping was performed on fresh culture isolates using the Pneumotest kit (Statens Serum Institut, Copenhagen, Denmark) which consisted of 12 pneumococcal pool antisera and different factor antisera. Figure 1. Comparison of IPD serotype distribution among paediatric (A) and adult IPD cases (B), 2009-2011 • Among adults, there was a wider serotype distribution than in children. Serotype 3, which has been found to be associated with significantly high case-fatality rates16, predominated, while the less predominant serotypes (6B, 8, 14, 19A, 23F) varied over the period 2009-2011 (Figure 1B). • The proportions of adult IPD cases potentially covered by serotypes contained in PCV7, PCV13 and PPV23 were 33%, 62.5% and 77.3% in 2011 (Figure 2B). • RESULTS AND DISCUSSION • Of 116 Streptococcus pneumoniae isolates, 93 (80.2%) were serotyped by NPHL and 23 (19.8%) were serotyped by KKH. The numbers of invasive pneumococcal isolates from paediatric and adult patients were 28 (24.1%) and 88 (75.9%), respectively. • Some isolates were from cerebrospinal fluid, pleural fluid, peritoneal fluid or tissues. The majority of isolates (90.5%) were obtained from blood culture specimens. • The most prevalent serotypes observed among children were type 19A (11 cases, 39.3%) and type 14 (6 cases, 21.4%). • Compared to data obtained the period 2009-2011, nonvaccine type 19A followed by types 14, 6B predominated in 2011, 2010 instead of the vaccine types 6B, 14 and 23F which were the most common in 2009 (Figure 1A). The non-PCV13 serotypes 6C, 15 and 23A were also observed. • The numbers of paediatric IPD cases that would be covered by PCV7, PCV10 and PCV13 were 9 (32.1%), 9 (32.1%) and 23 (82.1%), respectively. There appears to be a downward trend in the proportion of PCV7 serotypes among paediatric IPD cases: 80.1% (in 2009) decreasing to 50% (in 2010) then to 32.1% (in 2011) (Figure 2A). (B) (A) Figure 2. Potential coverage rates of PCV7, PVC13 and PPV23 for paediatric (A) and adult IPD cases (B), 2011 CONCLUSION Our results showed that the most predominant serotype observed among paediatric cases was 19A which is not covered by PCV7 vaccine. Since PCV13 was introduced in Singapore’s childhood immunization programme in December 2011, the majority of IPD paediatric cases were either immunized with PCV7 or not vaccinated. Continued surveillance is necessary to detect emerging serotypes after the introduction of 13-valent pneumococcal vaccine. REFERENCES 1. Pneumococcal conjugate vaccine for childhood immunization-WHO position paper. Wkly EpidemiolRec 2007;82:93-104.