title: Bacterial load of pneumococcal serotypes correlates with their prevalence and multiple serotypes is associated with acute respiratory infections among children less than 5 years of age.
abstract: BACKGROUND
  Among pneumococcal serotypes, some serotypes are more prevalent in the nasopharynx than others; determining factors for higher prevalence remain to be fully explored. As non-vaccine serotypes have emerged after the introduction of 7-valent conjugate vaccines, study of serotype specific epidemiology is in need. When two or more serotypes co-colonize, they evolve rapidly to defend host's immune responses; however, a clear association of co-colonization with a clinical outcome is lacking.
  
  
  METHODS
  Children less than 5 years old who were admitted to hospital due to acute respiratory infections (ARI) (n = 595) and healthy children (n = 350) were recruited. Carriage of pneumococcus was determined by culture and lytA PCR in the nasopharyngeal samples. Serotype/serogroup detection and its quantification were done by the nanofluidic real time PCR system. Spearman's correlation and logistic regression were used to examine a correlation of serotype/serogroup specific bacterial load with its prevalence and an association of co-colonization with ARI respectively.
  
  
  RESULTS
  Serotype/serogroup specific bacterial load was correlated with its prevalence, both in ARI cases (Spearman's rho = 0.44, n = 186; P<0.0001) and healthy children (Spearman's rho = 0.41, n = 115; P<0.0001). The prevalence of multiple serotypes was more common in ARI cases than in healthy children (18.5% vs 7.1%; aOR 2.92, 95% CI: 1.27-6.71; P = 0.01). The dominant serotype in the co-colonization had a 2 log10 higher bacterial load than the subdominant serotype, both in ARI cases (P<0.001) and healthy children (P<0.05).
  
  
  CONCLUSIONS
  High bacterial load in the nasopharynx may help transmit pneumococci among hosts, and increase the chance of successful acquisition and colonization. Co-colonization of multiple serotypes of pneumococci is linked with ARI, which infers the interactions of multiple serotypes may increase their pathogenicity; however, they may compete for growth in number.
authors.affiliation: Department of Clinical Medicine, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan; Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors.forename: Bhim Gopal
authors.initials: BG
authors.lastname: Dhoubhadel
authors.affiliation: Department of Clinical Medicine, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Yasunami
authors.affiliation: Department of Bacteriology, National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
authors.forename: Hien Anh Thi
authors.initials: HA
authors.lastname: Nguyen
authors.affiliation: Department of Clinical Medicine, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
authors.forename: Motoi
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: Department of Bacteriology, National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
authors.forename: Thu Huong
authors.initials: TH
authors.lastname: Vu
authors.affiliation: Department of Microbiology, Khanh Hoa General Hospital, NhaTrang, Vietnam.
authors.forename: Ai
authors.initials: A
authors.lastname: Thi Thuy Nguyen
authors.affiliation: Department of Bacteriology, National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
authors.forename: Duc Anh
authors.initials: DA
authors.lastname: Dang
authors.affiliation: Department of Pediatric Infectious Diseases, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
authors.forename: Lay-Myint
authors.initials: LM
authors.lastname: Yoshida
authors.affiliation: Department of Clinical Medicine, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan; Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors.forename: Koya
authors.initials: K
authors.lastname: Ariyoshi
mesh_terms: D000208:Acute Disease; D058491:Bacterial Load; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009305:Nasopharynx / Q000382:microbiology; D015995:Prevalence; D060888:Real-Time Polymerase Chain Reaction; D012141:Respiratory Tract Infections / Q000382:microbiology*; D065288:Serogroup; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology*