INTRODUCTIONWe investigated the 2005 outbreak of dengue fever (DF)/dengue haemorrhagic fever (DHF) to determine its epidemiological, virological and entomological features to further understand the unprecedented resurgence.

MATERIALS AND METHODSAll physician-diagnosed, laboratory-confirmed cases of DF/DHF notified to the Ministry of Health, Singapore during the outbreak as well as entomological and virological data were analysed retrospectively.

RESULTSA total of 14,006 cases of DF/DHF comprising 13,625 cases of DF and 381 cases of DHF, including 27 deaths were reported, giving an incidence rate of 322.6 per 100,000 and a case-fatality rate of 0.19%. The median age of the cases and deaths were 32 and 59.5 years, respectively. The incidence rate of those living in compound houses was more than twice that of residents living in public and private apartments. The distribution of DF/DHF cases was more closely associated with Aedes aegypti compared to Aedes albopictus breeding sites and the overall Aedes premises index was 1.15% (2.28% in compound houses and 0.33% to 0.8% in public and private apartments). The predominant dengue serotype was DEN-1. A significant correlation between weekly mean temperature and cases was noted. The correlation was strongest when the increase in temperature preceded rise in cases by a period of 18 weeks.

CONCLUSIONThe resurgence occurred in a highly densely populated city-state in the presence of low Aedes mosquito population. Factors contributing to this resurgence included lower herd immunity and change in dominant dengue serotype from DEN-2 to DEN-1. There was no evidence from gene sequencing of the dengue viruses that the epidemic was precipitated by the introduction of a new virulent strain. The current epidemiological situation is highly conducive to periodic dengue recurrences. A high degree of vigilance and active community participation in source reduction should be maintained.

Adult ; Aedes ; Animals ; Dengue ; epidemiology ; prevention & control ; transmission ; Dengue Virus ; immunology ; isolation & purification ; pathogenicity ; Disease Outbreaks ; Female ; Humans ; Immunity, Herd ; Incidence ; Insect Vectors ; Male ; Middle Aged ; Mosquito Control ; Primary Prevention ; methods ; Public Health ; Retrospective Studies ; Risk Factors ; Serotyping ; Singapore ; epidemiology

Severe acute respiratory syndrome (SARS) was imported into Singapore in late February 2003 by a local resident who returned from a holiday in Hong Kong and started an outbreak in the hospital where she was admitted on 1 March 2003. The disease subsequently spread to 4 other healthcare institutions and a vegetable wholesale centre. During the period between March and May 2003, 238 probable SARS cases, including 8 imported cases and 33 deaths, were reported. Transmission within the healthcare and household settings accounted for more than 90% of the cases. Factors contributing to the spread of infection included the failure to recognise the high infectivity of this novel infection, resulting in a delay in isolating initial cases and contacts and the implementation of personal protective measures in healthcare institutions; and the super-spreading events by 5 index cases, including 3 with co-morbid conditions presenting with atypical clinical manifestations of SARS. Key public health measures were directed at prevention and control within the community and hospitals, and the prevention of imported and exported cases. An isolated laboratory-acquired case of SARS was reported on 8 September 2003. Based on the lessons learnt, Singapore has further strengthened its operational readiness and laboratory safety to respond to SARS, avian flu and other emerging diseases.
Adolescent ; Adult ; Aged ; Aged, 80 and over ; Child ; Child, Preschool ; Disease Outbreaks ; prevention & control ; statistics & numerical data ; Disease Transmission, Infectious ; prevention & control ; Female ; Humans ; Infant ; Infant, Newborn ; Male ; Middle Aged ; Retrospective Studies ; Severe Acute Respiratory Syndrome ; epidemiology ; transmission ; Singapore ; epidemiology