اپیدمی تب مخملک، هنگ کنگ، سال ۲۰۱۱ Scarlet Fever Epidemic, Hong Kong, 2011

The Study Scarlet fever is a statutory notifi able disease in Hong Kong. A clinical case is defi ned as illness in a person who has clinical features of scarlet fever (fever and fi ne, sandpaper rash of characteristic distribution that blanches on pressure, with or without strawberry tongue, desquamation, or sore throat). A confi rmed case is defi ned as a clinical case with positive throat or wound culture for S. pyogenes or antistreptolysin titer >200. Epidemiologic, clinical, and laboratory data were collected by standard questionnaire for every reported case. A cluster was defi ned as >2 cases in persons sharing the same residential or school address within the incubation period. We compared epidemiologic, clinical, and microbiological features of the scarlet fever cases from January–July 2011 (outbreak period) with features of those reported during 2008–۲۰۱۰ (baseline period). We used SPSS version 14.0 (SPSS Inc., Chicago, IL, USA) for analyses; p<0.05 was considered signifi cant. For comparison, we performed a retrospective review of hospital discharge records kept by public hospitals. We extracted records of patients hospitalized during January 2008–July 2011 who had diagnoses that are known complications of scarlet fever, including toxic shock syndrome, acute rheumatic fever, and acute glomerulonephritis. These cases were reviewed to determine whether the complications were related to scarlet fever. Bacterial culture of S. pyogenes was performed on diagnostic specimens in hospital laboratories and the Public Health Laboratory Centre of the Department of Health; the latter serves as the diagnostic and public health reference laboratory in Hong Kong. Antimicrobial drug susceptibility testing, emm typing, and detection of various virulence genes were performed at the Public Health Laboratory Centre on S. pyogenes isolates received during 2011 and archived during 2008–۲۰۱۰ (۱). Pulsed-fi eld gel electrophoresis (PFGE) was performed on the basis of the gram-positive protocol, and PFGE profi les were analyzed by using BioNumerics 5.0 software (Applied Maths, SintMartens-Latem, Belgium). In June 2011, the Department of Microbiology of the University of Hong Kong announced the discovery of a unique 48-kb insertion sequence in the genome of S. pyogenes isolated from a blood specimen from a 7-year-old girl who died of scarlet fever (2). We tested for this insert in a sample of strains collected during 2008–۲۰۱۱ using the method provided by the University of Hong Kong. During January 1–July 31, 2011, a total of 996 cases of scarlet fever were reported, greatly exceeding the annual number of cases reported during 2008 (235), 2009 (187), and 2010 (128). Outbreak activity in 2011 peaked at week 26 (week ending June 25) (Figure 1). During the outbreak period (January–July 2011), the annualized incidence rate was 24.0/100,000 population, ≈۹× higher than the average annualized incidence rate of 2.62/100,000 population during the baseline period of 2008–۲۰۱۰٫ During the previous 2 decades, baseline annual incidence rates ranged from 0.0351 to 3.37 cases/100,000 population. Table 1 compares the epidemiologic features, clinical features, and laboratory results for scarlet fever cases reported during 2011 and 2008–۲۰۱۰٫ Highest incidence (547 cases/100,000 population) was reported for children 4–۷ years of age (Table 1). Clinical features, complications, and case-fatality rate for cases reported in 2011 were largely comparable to those reported during the baseline period. The proportion of case-patients requiring hospitalization during 2011 was lower, and mean duration of hospital stay was ≈۰٫۵ days shorter than for the baseline period. Details of the 9 complicated cases are shown in Table 2.