Epidemiological analysis of non-M-typeable group A Streptococcus isolates from a Thai population in northern Thailand

Infection with group A streptococci (GAS) can lead to the development of se vere postinfectious sequelae such as rheumatic fever (RF), In Thailand, RF and rheumatic heart disease (RHD) remain important health problems. More th an 80% of GAS circulating in this population are non-M antigen typeable by conventional M serotyping methods. In this study, we determine the M protei n sequence types of GAS isolates found in northern Thailand. The emm genes from 53 GAS isolates, collected between 1985 and 1995 from individuals with pharyngitis, impetigo, acute RF (ARF), RHD, or meningitis as well as from individuals without infections, were amplified by PCR and sequenced. Thirte en new sequence types that did not show homology to previously published se quences were characterized. Six of these sequence types could be isolated f rom both skin and throat sites of impetigo and pharyngitis/ARF patients, re spectively, In many cases we could not specifically differentiate skin stra ins or throat strains that could be associated with ARF or acute glomerulon ephritis. Antigenic variations in the emm gene of the isolates investigated , compared to published M protein sequences, were predominantly due to poin t mutations, small deletions, and insertions in the hypervariable region, O ne group of isolates with homology to M44 exhibited corrected frameshift mu tations. A new M type isolated from an RHD patient exhibited nucleotide seq uence corresponding to the N terminus of M58 and the C terminus of M25, sug gesting that recombination between the two types may have occurred. This st udy provided epidemiological data relating to GBS endemic to northern Thail and which could be useful for identification of vaccine candidates in a spe cific region of endemicity.