An epidemic of dengue 3 in far north Queensland, 1997-1999

Objectives: To describe an epidemic of dengue type 3 that occurred in far north Queensland in 1997-1999 and its influence on the further development of dengue prevention and control strategies. Design: Epidemiological and laboratory investigation of cases, entomological surveys and phylogenetic analysis of dengue virus isolates. Main outcome measures: Numbers and characteristics of confirmed cases; Breteau Index (BI; number of containers breeding Aedes aegypti per 100 premises); effect of control measures on mosquito populations; genetic homology of epidemic virus with other dengue virus isolates. Results: The epidemic lasted 70 weeks and comprised 498 confirmed cases in three towns (Cairns, Port Douglas and Mossman); 101 patients (20%) were admitted to hospital. Median interval between symptom onset and notification was seven days (range, 0-53 days), and cumulative duration of viraemia of public health significance was 2072 days. Bls in affected areas were high, particularly in Mossman (45) and Port Douglas (31), Control measures significantly reduced mosquito populations (assessed as number of ovitraps containing Ae. aegypti eggs and mean number of eggs per trap [P < 0.05 for both]). However, transmission persisted in several foci, in part due to undetected waterfilled containers breeding Ae, aegypti. The epidemic virus belonged to serotype 3; phylogenetic analysis suggested it was imported from Thailand. Conclusions: The epidemic had greater morbidity than other recent Queensland epidemics of dengue and was harder to control, necessitating substantial revision of the Dengue Fever Management Plan for North Queensland. The epidemic's severity supports the hypothesis that dengue viruses from South East Asia are more virulent than others.