Active surveillance of invasive group A streptococcus and emm typing in New Mexico, 2004-2007

New Mexico began conducting active, laboratory, population-based surveillance for invasive group A streptococcus (GAS) in 2004 as part of the CDC's Emerging Infections Program (EIP). NM, which shares borders with 5 U.S. states and 2 Mexican states, has the highest percentage of Hispanics (43%) and the third highest of Native Americans in the U.S. From 2004 through 2007, 420 laboratory-confirmed cases of GAS were identified. Morbidity ranged from 4.8 cases per 100,000 population in 2004 to 5.3 per 100,000 population in 2007, slightly higher than reported nationally (3.3, 3.8). Rates were highest among individuals over the age of 64 years (12.3 per 100,000 population), American Indians (9.1 per 100,000 population), and Hispanics (3.9 per 100,000 population). The proportion of cases associated with necrotizing fasciitis was similar to national rates for the first 3 years, but almost doubled (12.9% vs. 6.2%) in 2007. Eighty-four percent of cases were hospitalized, with a median length of stay of 7 days (IQ25=4, IQ75=14). Seventeen percent of patients died from GAS disease. The 5 most common emm types (1, 76, 3, 12, and 28) accounted for 53% of isolates. This is comparable to national data with the exception of emm type 76. Emm type 76, not seen in 2004 or 2005 in NM, accounted for 3% of isolates in 2006 and 8% in 2007. Further analysis will be conducted to better understand the high incidence rates among the older age-group, Native Americans, Hispanics, and the emergence of emm type 76.