Abstract
BackgroundGroup A streptococcus (GAS) is the most frequent cause of bacterial pharyngitis in school-aged children. The postinfection sequel as acute rheumatic fever (ARF) and rheumatic heart disease that cause morbidity and mortality among young people is public health concerns in several developing countries. Asymptomatic carriage state of GAS is not fully understood in terms of host and bacterial factors. Although the ability of transmitting GAS of the asymptomatic carriers is relatively low, they may present the reservoir of the epidemic. A fraction of GAS carriers is difficult to estimate in practice and may greatly vary between populations. Understanding the role of carriage on the transmission dynamic of GAS is important for assessing the public health impact of the ARF.MethodThis study investigates the effect of GAS carriers on both the transmission and dynamic of ARF cases by using a mathematical model.ResultWe derive the sufficient conditions for which the GAS can spread or extinct from the naive population under the variation of the fraction of symptomatic cases over the incidence of GAS. The threshold is possible to occur in general, but the last condition which is rather restrictive and involves parameter uncertainty. The increasing of carriers in the endemic state leads to the reduction in magnitude of the reproduction number and the number of ARF patients. We demonstrate that the adjustment of parameters can be carried out by the use of endemic state and some specific data.ConclusionWe show theoretically that the presence of asymptomatic carriers may induce the epidemic threshold and reduce the virulence of GAS and the prevalence of ARF.
Highlights
Group A streptococcus (GAS) is the most frequent cause of bacterial pharyngitis in school-aged children
We show theoretically that the presence of asymptomatic carriers may induce the epidemic threshold and reduce the virulence of GAS and the prevalence of acute rheumatic fever (ARF)
Acute Rheumatic Fever (ARF) is an inflammatory disease which developed as a sequel of group A β-hemolytic streptococcal (GAS) pharyngitis [1,2,3]
Summary
Group A streptococcus (GAS) is the most frequent cause of bacterial pharyngitis in school-aged children. The postinfection sequel as acute rheumatic fever (ARF) and rheumatic heart disease that cause morbidity and mortality among young people is public health concerns in several developing countries. Among the ARF patients, the rheumatic heart disease is a major cause of morbidity and mortality among children and young people (between 5-15 years of age). It was estimated that 5–15% of school-aged children harbor GAS in pharynx but do not Yokchoo et al Theoretical Biology and Medical Modelling (2019) 16:14 develop symptom. These may be characterized as a carriage state of GAS [8,9,10]. Since the carriers do not have GAS symptom, except for the common symptoms caused by viral infection, the evaluation of the fraction of carriers among the population under study may be obscure
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