Oral Presentation 20th Lancefield International Symposium on Streptococci and Streptococcal Diseases 2017

What can a million throat swabs tell us about the distribution of group A Streptococcus and acute rheumatic fever? (#77)

Jane Oliver 1 , Arlo Upton 2 , Nevil Pierse 1 , Deborah Williamson 3 , Michael G Baker 1
  1. University of Otago Wellington, Newtown/Wellington, WELLINGTON, New Zealand
  2. Labtests NZ, Auckland, New Zealand
  3. Department of Microbiology and Immunology, Peter Doherty Institute, University of Melbourne , Melbourne, Australia

Acute rheumatic fever (ARF) produces an important burden of disease in New Zealand (NZ) Māori and Pacific populations. Operation of New Zealand’s Rheumatic Fever Prevention Programme (RFPP) resulted in large scale throat swabbing and testing for Group A Streptococcus (GAS) pharyngitis, which can trigger ARF. Our aim was to describe the distribution of GAS in Auckland and comment on its correlation with ARF incidence.

Throat swab data collected from Auckland primary healthcare clinics (PHC) and schools were obtained (2010-2016). Descriptive epidemiological summary statistics were generated covering swab numbers, population incidences of swabbing and GAS, and GAS+ve swab proportion.

Altogether 1,257,058 throat swabs were collected. Swabbing and GAS+ve proportion peaked in age groups with highest ARF risk (5-14 year olds). GAS+ve proportion was similar between ethnic groups (~19%), however GAS incidence was highest in Pacific (81.9/1,000 child-years) and Maori (60.4/1,000 child-years). Similarly, GAS incidence was highest in the most deprived group (84.7/1,000 child-years), yet GAS+ve proportion was similar across socioeconomic quintiles. GAS incidence peaked in winter and was lowest in summer, yet GAS+ve proportion was highest in summer (%).

The RFPP greatly increased swabbing and testing of populations at high risk of ARF, but dramatically increased swabbing (and antibiotic treatment) in low-risk groups. There is a broad correlation between GAS population load and ARF risk, however ethnic and socioeconomic disparities in ARF are much more pronounced. Therefore, factors besides the distribution of GAS culture-positive pharyngitis influence the epidemiology of ARF in NZ.