Globally, there is wide variation in streptococcal titer upper limits of normal (ULN) for antistreptolysin O (ASO) and anti-deoxyribonuclease B (ADB) used as an evidence of recent group A streptococcal infection to diagnose acute rheumatic fever (ARF).
We audited ASO and ADB titers among individuals with ARF in New Zealand (NZ) and in Australia’s Northern Territory. We summarized streptococcal titers by different ARF clinical manifestations, assessed application of locally recommended serology guidelines where NZ uses high ULN cut-offs and calculated the proportion of cases fulfilling alternative serologic diagnostic criteria.
From January 2013 to December 2015, group A streptococcal serology results were available for 350 patients diagnosed with ARF in NZ and 182 patients in Northern Territory. Median peak streptococcal titers were similar in both settings. Among NZ cases, 267/350 (76.3%) met NZ serologic diagnostic criteria, whereas 329/350 (94.0%) met Australian criteria. By applying Australian ULN titer cut-off criteria to NZ cases, excluding chorea, ARF definite cases would increase by 17.6% representing 47 cases.
ASO and ADB values were similar in these settings. Use of high ULN cut-offs potentially undercounts definite and probable ARF diagnoses. We recommend NZ and other high-burden settings to use globally accepted, age-specific, lower serologic cut-offs to avoid misclassification of ARF.
From the *Centre for International Health, Department of Preventive and Social Medicine, University of Otago, Dunedin, New Zealand
†Institute of Environmental Science and Research, Wellington, New Zealand
‡School of Medical Sciences and Maurice Wilkins Centre, University of Auckland, Auckland, New Zealand
§Royal Darwin Hospital
¶Northern Territory Rheumatic Heart Disease Control Program
‖Global and Tropical Health, Menzies School of Health Research, Darwin, Northern Territory, Australia.
Accepted for publication September 6, 2018.
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N.J.M. is supported for a Senior Research Fellowship from the New Zealand Heart Foundation, and A.P.R. is supported by an Australian National Health and Medical Research Council fellowship (1113638). Institute of Environmental Science and Research Limited (ESR) is funded by the New Zealand Ministry of Health to undertake surveillance of ARF. The other authors have no conflicts of interest to disclose.
Address for correspondence: Susan Jack, PhD, Department of Preventive and Social Medicine, University of Otago, 18 Frederick Street, Dunedin 9016, New Zealand. E-mail: firstname.lastname@example.org.