Colony morphology of Group A Streptococcus. Credit: ICDC, China CDC

Transmission electron microscopy of Group A Streptococcus. Credit: ICDC, China CDC

Comprehensive surveillance is needed to monitor human disease epidemics, according to Chinese and Australian researchers analysing a Chinese outbreak of the highly infectious childhood disease, scarlet fever.

Study co-author, Director of The University of Queensland’s Australian Infectious Diseases Centre Professor Mark Walker said the 2011-2016 outbreak disease incidence was almost three times higher than that seen in the past 30 years.

Study first author Dr Yuanhai You said the Chinese Center for Disease Control and Prevention (China CDC) in Beijing continued to investigate underlying reasons for the outbreak against a background of rapid development of the Chinese economy; improvement in the national health system; and increasing mobility of Chinese domestic and international populations

Deputy Director of The National Institute for Communicable Disease Control and Prevention, China CDC Professor Jianzhong Zhang said many factors may have interacted.

“They include disease-causing streptococcal isolates, environmental factors, climate, living standards, population movement, host population genetics and herd immunity which may have influenced changes in the numbers and geographic distribution of cases,” he said.

Professor Walker said scarlet fever outbreaks began in 2011 in mainland China, Hong Kong, and South Korea, and in 2014 an epidemic was reported in the United Kingdom, although there has not yet been an Australian outbreak.

Dr You said despite the epidemic lasting over six years, there had not been a comprehensive nationwide epidemiological description at its epicenter. The new study, led by the China CDC, used epidemiological data and molecular analysis to address this issue.

Researchers found the highest incidence in the Chinese outbreak in children aged five years, with kindergarten children accounting for 44 per cent of cases. The highest incidence was reported in males in May and June (early summer) and December (winter), in Beijing, Shanghai and northern provinces.

The study also collected historical and outbreak-related strains of the disease-causing bacteria from distinct geographic regions of mainland China, and used whole genome sequencing to gain insight into genomic evolution, virulence and antimicrobial resistance.

Professor Walker said the study compared information from the Chinese outbreak with information collected from Hong Kong and UK outbreaks.

The new study identified antibiotic-resistant bacterial strains, and found Hong Kong strains in mainland China, suggesting a role in selection and expansion of scarlet fever lineages in China.

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