An outbreak investigation of scrub typhus in Western Province, Solomon Islands, 2014

OBJECTIVE: To identify the etiology and risk factors of undifferentiated fever in a cluster of patients in Western Province, Solomon Islands, May 2014. METHODS: An outbreak investigation with a case control study was conducted. A case was defined as an inpatient in one hospital in Western Province, Solomon Islands with high fever (> 38.5 °C) and a negative malaria microscopy test admitted between 1 and 31 May 2014. Asymptomatic controls matched with the cases residentially were recruited in a ratio of 1:2. Serum samples from the subjects were tested for rickettsial infections using indirect micro-immunofluorescence assay. RESULTS: Nine cases met the outbreak case definition. All cases were male. An eschar was noted in five cases (55%), and one developed pneumonitis. We did not identify any environmental factors associated with illness. Serum samples of all five follow-up cases (100%) had strong-positive IgG responses to scrub typhus. All but one control (10%) had a moderate response against scrub typhus. Four controls had low levels of antibodies against spotted fever group rickettsia, and only one had a low-level response to typhus group rickettsia. DISCUSSION: This outbreak represents the first laboratory-confirmed outbreak of scrub typhus in the Western Province of Solomon Islands. The results suggest that rickettsial infections are more common than currently recognized as a cause of an acute febrile illness. A revised clinical case definition for rickettsial infections and treatment guidelines were developed and shared with provincial health staff for better surveillance and response to future outbreaks of a similar kind.

A serological survey of rickettsial infections in the Gazelle Peninsula, East New Britain and a review of the literature

Of the various rickettsial diseases, only scrub typhus has been well documented in Papua New Guinea. A review of the historical literature confirms this. A serological survey was conducted on 113 antenatal patients presenting to a district hospital in Kokopo, East New Britain. Results suggested that a spotted fever rickettsial infection is common in this area with a seroprevalence of about 17% in young women. There was no evidence of scrub typhus or murine (endemic) typhus in the population sampled. Clinical implications of these findings are discussed.