Nasopharyngeal carriage of penicillin-resistant Streptococcus pneumoniae among children with acute respiratory tract infections in Thailand: a molecular epidemiological survey

The prevalence of penicillin-resistant Streptococcus pneumoniae in Thailand has dramatically increased over the last decade. During a national survey, which was conducted from 1992 to 1994, 37.2% of the pneumococci isolated f rom the nasopharynges of children with acute respiratory tract infections w ere penicillin resistant (MIC, greater than or equal to 0.1 mu g/ml). In or der to investigate the prevalence and clonal relatedness of nasopharyngeal carriage of penicillin-resistant S. pneumoniae in Thailand, a molecular epi demiological survey was undertaken. To this end, 53 penicillin-resistant pn eumococcal isolates from children who suffered from acute respiratory tract infections and who originated from five distinct regions of the country we re characterized in detail. DNA fingerprint analysis demonstrated 13 cluste rs, i.e., genotypes shared by two or more strains, and 14 unique genotypes. The cluster size varied from 2 (nine clusters) to 11 strains (one cluster) . Six of the 13 restriction fragment end labeling clusters consisted of two or more distinct serotypes, indicating frequent horizontal transfer of cap sular genes. Geographical distribution of the genotypes among the five regi ons of Thailand demonstrated that only four genetic clusters were restricte d to single areas of the country, whereas the other nine clusters represent ed isolates collected in two or more districts. These observations demonstr ate that the majority of the genetic clusters are spread throughout the cou ntry. The must predominant genetic cluster representing 21% of the isolates , was identical to the Spanish pandemic clone 23F. In addition, the second largest cluster matched the Spanish-French international clone 9V. These da ta indicate that the genetic clones 23F and 9V, which are widely spread thr oughout the world, are the most predominant multidrug-resistant pneumococca l clones in Thailand. Therefore, we conclude that these pandemic clones are primarily responsible for the increase in the prevalence of pneumococcal p enicillin resistance in Thailand.