Objectives: To investigate two outbreaks of dengue type 2 in north Queensland, one in the Torres Strait beginning in late 1996, the other in a Cairns suburb in early 1997.
Design: Epidemiological investigation of all laboratory‐confirmed cases of dengue, entomological investigation of the local environment, and laboratory analysis of the isolated dengue viruses.
Main outcome measures: Numbers of confirmed and of locally acquired cases; virus serotype; comparison of nucleotide sequences between viruses isolated from the two outbreaks; and Breteau Index (Bl = number of containers with larvae of the mosquito vector Aedes aegypti found per 100 houses investigated) on the affected islands and in the Cairns suburb.
Results: There were 201 confirmed cases of dengue in the Torres Strait outbreak, which lasted nearly seven months, and seven confirmed cases in the Cairns outbreak, which lasted about nearly 11 weeks. Most (190) were confirmed as dengue type 2. Nucleotide sequencing of viruses isolated from the two outbreaks showed they were identical. Ae. aegypti breeding sites were very common on the five Torres Strait islands surveyed (Bis, 73‐219 ‐ high risk), but less so in the Cairns suburb (Bl, 23). The most common breeding sites were water storage reservoirs, particularly rainwater tanks, on the outer Torres Strait islands, discarded containers (such as plastic containers, buckets and tyres) on Thursday Island, and garden items (such as flowerpot bases and jars) in Cairns.
Conclusions: The virus responsible for the Cairns outbreak was most probably introduced from the Torres Strait, whereas the virus responsible for the Torres Strait outbreak was imported from Papua New Guinea. Preventive strategies tailored to specific locations are needed to reduce breeding of Ae. aegypti in north Queensland, and the consequent risk of future outbreaks of dengue.
We report 3 cases of spotted fever group rickettsial infection (presumed Queensland tick typhus) in residents of northern Queensland, Australia, who had unusually severe clinical manifestations. Complications included renal failure, purpura fulminans, and severe pneumonia. Clinical illness caused by Rickettsia australis may not be as benign as previously described.
Scrub typhus, caused by
Orientia tsutsugamushi
, occurs throughout Southeast Asia. We descript ten cases that occurred in the Torres Strait islands of northern Australia during 2000 and 2001. Preceding heavy rain may have contributed to the outbreak. The successful use of azithromycin in two pediatric patients is also reported.
An epidemic of dengue type 2 infection occurred in North Queensland during 1992 and 1993. A random serosurvey of 1,000 residents of a population that experienced this epidemic only during 1993 was conducted to determine the proportion of the population at risk for secondary infection in the event of another epidemic with a different serotype. The ability of an ELISA to detect prior exposure to the dengue virus was compared with the hemagglutination inhibition assay. Dengue 2 virus plaque-reduction neutralization assays were performed to evaluate the specificity of the antibody response. Antibodies to dengue virus, or closely related flaviviruses, were detected in 61.9%. Seroprevalence increased with age and correlated well with known previous epidemics in the region. The sensitivity and specificity of the ELISA was 99.2% and 96.2%, respectively. An estimated 26% of the population was infected during the 1993 epidemic.
Dengue fever is caused by one of the four serotypes of the dengue virus and is transmitted by the urban mosquito Aedes aegypti. In 1993, the city of Charters Towers in the tropical north of Australia experienced an epidemic caused by the dengue 2 virus. A cross-sectional sample of 1,000 people was assessed for determinants of recent symptomatic dengue infection. After exclusion of people with prior exposure to dengue 2, a study group of 797 persons, including 196 patients with recent infection, were evaluated. Stepwise logistic regression analysis identified four determinants of infection: the presence of a case of dengue fever within two residential blocks (odds ratio (OR) = 3.61, 95% confidence interval (CI) 2.56-5.10), house screening (OR = 0.60, 95% CI 0.40-0.89), the presence of a water tank within two residential blocks (OR = 1.51, 95% CI 1.02-2.22), and the use of knockdown insecticide (OR = 1.75, 95% CI 1.22-2.51). Classification and Regression Tree analysis identified a group of 152 individuals in whom the prevalence of dengue infection was 50%. These people lived within two blocks of a suspected dengue fever case, did not have house screening, and used knockdown sprays. If dengue had not occurred within two residential blocks, there were no additional factors that significantly influenced the prevalence of dengue fever. Control of dengue epidemics should involve attempts to geographically contain the spread of infection, use of house screening, and the removal of mosquito breeding sites such as water tanks.
The objective of this study wasto determine the epidemiological significance of subterranean mosquito breeding sites to the 1993 outbreak of dengue fever (type 2) in the northern Queensland town of Charters Towers, Australia. In recent studies on subterranean mosquito breeding, containers such as wells and service manholes have been shown to be important breeding sites to Australia's only dengue vector, Aedes aegypti (L.). This study demonstrates a direct epidemiological association between subterranean breeding sites and dengue virus infection. The mean distance between residents seropositive for dengue 2 and the nearest subterranean container (113 m) was significantly less than for a randomly selected control (191 m), (F = 81.9; df = 1, 478; P < 0.001). Residents positive for dengue 2 antibodies was 2.47 (95% confidence interval 1.88-3.24) times higher for those living within 160 m of a well or service manhole, compared with those residing further away. These findings emphasize the importance of incluuding subterranean water containers in Ae. aegypti surveillance and control programs.
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