Research Article: Serotype Distribution of Clinical Streptococcus pneumoniae Isolates before the Introduction of the 13-Valent Pneumococcal Conjugate Vaccine in Cambodia

Date Published: March 08, 2018

Publisher: The American Society of Tropical Medicine and Hygiene

Author(s): Malin Inghammar, Youlet By, Christina Farris, Thong Phe, Laurence Borand, Alexandra Kerleguer, Sophie Goyet, Vonthanak Saphonn, Chanleakhena Phoeung, Sirenda Vong, Blandine Rammaert, Charles Mayaud, Bertrand Guillard, Chadwick Yasuda, Matthew R. Kasper, Gavin Ford, Steven W. Newell, Ung Sam An, Buth Sokhal, Sok Touch, Paul Turner, Jan Jacobs, Mélina Messaoudi, Florence Komurian-Pradel, Arnaud Tarantola.


Childhood vaccination with the 13-valent pneumococcal conjugate vaccine (PCV13) was introduced in Cambodia in January 2015. Baseline data regarding circulating serotypes are scarce. All microbiology laboratories in Cambodia were contacted for identification of stored isolates of Streptococcus pneumoniae from clinical specimens taken before the introduction of PCV13. Available isolates were serotyped using a multiplex polymerase chain reaction method. Among 166 identified isolates available for serotyping from patients with pneumococcal disease, 4% were isolated from upper respiratory samples and 80% were from lower respiratory samples, and 16% were invasive isolates. PCV13 serotypes accounted for 60% (95% confidence interval [CI] 52–67) of all isolates; 56% (95% CI 48–64) of noninvasive and 77% (95% CI 57–89) of invasive isolates. Antibiotic resistance was more common among PCV13 serotypes. This study of clinical S. pneumoniae isolates supports the potential for high reduction in pneumococcal disease burden and may serve as baseline data for future monitoring of S. pneumoniae serotypes circulation after implementation of PCV13 childhood vaccination in Cambodia.

Partial Text

Streptococcus pneumoniae (pneumococci) cause a wide spectrum of infections, ranging from invasive disease with a high case-fatality rate to asymptomatic colonization. Despite available antibiotics, it is estimated that around 800,000 children die every year due to pneumococcal disease, especially in developing countries where timely access to adequate health care is limited.1

All principal microbiological laboratories in Cambodia were contacted for identification of stored isolates of S. pneumoniae from specimens taken before January 2015 (i.e., before the introduction of PCV13). Stored strains were identified at 1) Institut Pasteur du Cambodge (IPC), Phnom Penh, as part of the Surveillance and investigation of Epidemics in South-East Asia (SISEA) project, a prospective study of lower respiratory infections in two provincial hospitals (Takeo and Kampong Cham provinces),13 as well as from routine cultures performed from 2006 to 2014; 2) Sihanouk Hospital Center of Hope (SHCH), Phnom Penh, systematically collected as part of a microbiological surveillance program “Surveillance of antimicrobial resistance among consecutive blood culture isolates in tropical settings,” 2008 through 2014; 3) Naval Medical Research Unit No. 2 (NAMRU 2), Phnom Penh, as part of a prospective surveillance study “Surveillance and Etiology of Acute Undifferentiated Febrile Illnesses in Cambodia” (Kandal, Kampong Speu, Kratie, Ratanakiri, Stung Treng, and Svay Rieng), 2005–2014. An overview of the origin of isolates and the participating microbiological laboratories are listed in Table 1. The laboratories at the following hospitals were contacted but none of them had any stored pneumococcal isolates from the study time period: National Pediatric Hospital; Kampong Cham; Takeo; Kampot; Battambang; Siem Reap; Calmette; Khmer Soviet; Kossamak; or Kantha Bopha.

In total, 249 isolates were identified at the participating institutions: 215 from IPC, 16 from SHCH, and 18 from NAMRU 2. Of these, we were unable to determine the serotype of 79 (32%) isolates because of sample contamination or degradation, four isolates were excluded as they stem from the same patient and index date, leaving 166 (67%) isolates in the analysis. Of these, 133 (80%) came from IPC, 15 (9%) from SHCH, and 18 (11%) from NAMRU 2. The basic characteristics of the isolates are shown in Table 2. Information on sex was available for 106/166 isolates.

Data from this retrospective study of clinical pneumococcal isolates in Cambodia, collected before the introduction of PCV13 in 2015, suggest that this vaccine potentially covers around 80% of the invasive isolates and around 60% of the noninvasive isolates. The range of serotypes and predicted vaccine coverage is consistent with the two studies previously published. A survey (2013–2014) reported 63% PCV13 coverage in colonizing isolates in pediatric outpatients (N = 601) in Cambodia,12 and 88% among invasive isolates (N = 40). A second study from the same center based on invasive isolates (N = 50) 2008–2012 predicted 92% PCV13 coverage.11 Furthermore, a review of studies from neighboring countries in Southeast Asia, including both pediatric and adult data, estimated that PCV13 provides 46–72% coverage for the circulating isolates.18




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