Emm type distribution of group A streptococcus isolates from the throat swabs of children living in areas with a high (Northland and Gisborne) or low (Palmerston North) incidence of acute rheumatic fever.

AIM: To assess the circulating emm types of pharyngeal isolates of group A streptococcus (GAS) among school children living in Northland, the Gisborne region and Palmerston North, New Zealand.

METHODS: GAS were isolated from throat swabs sent to laboratories in Northland (197 in 2013) and Gisborne (115 in 2014-15) and from children enrolled in the Palmerston North Solar Ventilation Project (70 in 2013-14). The incidences of acute rheumatic fever (ARF) cases in the three regions in 2014 were 9, 19.1 and 0 cases per 100,000 for Northland, the Gisborne region and Palmerston North respectively. DNA sequencing of the N-terminal portion of the emm gene was performed at the Institute of Environmental Science and Research Limited (ESR) laboratory (Porirua, New Zealand).

RESULTS: A total of 36 emm types were found among pharyngeal GAS isolates from Northland children with emm1 predominating (24%), 28 emm types from the Gisborne region with emm12 predominating (25%) and 20 emm types from Palmerston North, again with emm12 predominating (36%). Of these GAS isolates, 38% were emm pattern A-C, usually associated with throat infections, 23% were pattern D, usually associated with skin infections, and 39% pattern E or generalists. The most common of the 13 emm clusters detected were A-C4 (emm12; 18% isolates), A-C3 (emm1, emm227, emm238; 17% isolates), D4 (9 emm types; 16% isolates), E4 and E3 (8 emm types each; 15% and 10% isolates respectively). A total of 301 of the 376 (80%) isolates were serotypes previously associated with ARF in New Zealand.

CONCLUSION: The only significant differences in distribution between the regions with high (Northland and Gisborne area) and low (Palmerston North) incidences of ARF were the presence of emm3 and absence of emm41 among GAS isolates from Palmerston North school children.