Entomologic and molecular investigation into Plasmodium vivax transmission in Singapore, 2009

<p>Abstract</p> <p>Background</p> <p>Singapore has been certified malaria free since November 1982 by the World Health Organization and despite occasional local transmission, the country has maintained the standing. In 2009, three clusters of malaria cases were reported in Singapore.</p> <p>Methods</p> <p>Epidemiological, entomological and molecular studies were carried out to investigate the three clusters, namely Mandai-Sungei Kadut, Jurong Island and Sembawang.</p> <p>Results</p> <p>A total of 29 malaria patients, with no recent travel history, were reported in the three clusters. Molecular analysis based on the <it>msp3α </it>and <it>msp1 </it>genes showed two independent local transmissions: one in Mandai-Sungei Kadut and another in Sembawang. Almost all cases within each cluster were epidemiologically linked. In Jurong Island cluster, epidemiological link remains uncertain, as almost all cases had a unique genetic profile. Only two cases shared a common profile and were found to be linked to the Mandai-Sungei Kadut cluster. Entomological investigation found <it>Anopheles sinensis </it>to be the predominant Anopheline in the two areas where local transmission of <it>P. vivax </it>was confirmed. <it>Anopheles sinensis </it>was found to be attracted to human bait and bites as early as 19:45 hrs. However, all <it>Anopheles </it>mosquitoes caught were negative for sporozoites and oocysts by dissection.</p> <p>Conclusion</p> <p>Investigation of <it>P. vivax </it>cases from the three cluster areas confirmed the occurrence of local transmission in two areas. Although <it>An. sinensis </it>was the predominant Anopheline found in areas with confirmed transmission, the vector/s responsible for the outbreaks still remains cryptic.</p

An outbreak of gastroenteritis caused by Salmonella enterica serotype Enteritidis traced to cream cakes

Introduction: This paper describes the epidemiological, microbiological and environmental investigations conducted during an outbreak of Salmonella gastroenteritis in Singapore.Methods: A case-control study was undertaken to identify the vehicle of transmission. Microbiological testing was performed on faecal, food and environmental samples. Isolates of Salmonella were further characterized by phage typing and ribotyping.Results: There were 216 gastroenteritis cases reported from 20 November to 4 December 2007. The causative agent was identified as Salmonella enterica subspecies enterica serotype Enteritidis for 14 out of 20 cases tested. The vehicle of transmission was traced to cream cakes produced by a bakery and sold at its retail outlets (P < 0.001, OR = 143.00, 95% Cl = 27.23–759.10). More than two-thirds of the 40 Salmonella strains isolated from hospitalized cases, food samples and asymptomatic food handlers were of phage type 1; the others reacted but did not conform to any phage type. The phage types correlated well with their unique antibiograms. The ribotype patterns of 22 selected isolates tested were highly similar, indicating genetic relatedness. The dendrogram of the strains from the outbreak showed distinct clustering and correlation compared to the non-outbreak strains, confirming a common source of infection.Discussion: The cream cakes were likely contaminated by one of the ingredients used in the icing. Cross-contamination down the production line and subsequent storage of cakes at ambient temperatures for a prolonged period before consumption could have resulted in the outbreak