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.

Yaws is a chronic infectious disease caused by Treponema pallidum subsp. pertenue, which causes disease of the skin, bones and joints and is spread by skin-to-skin contact. Most cases are seen in young children living in rural remote communities in coastal areas. A major campaign to eradicate yaws between 1953 and 1958, by mass treatment of affected communities with long-acting, injectable penicillin, reduced the number of cases by 95% in Papua New Guinea (PNG), but yaws has reappeared in recent years. In the period 2008- 2015 PNG reported >25,000 cases per year, and the country is currently home to about 40% of all the cases of yaws in the world. In 2012, one oral dose of azithromycin was shown to be as effective as intramuscular penicillin in the treatment of the disease, and the World Health Organization launched a new initiative to eradicate yaws by 2020. The new treatment policy recommends mass azithromycin treatment of the entire population in endemic areas. Continued vigilance for the development of macrolide resistance in T. pallidum ssp. pertenue will be important as the drug is introduced into public health practice.