Table 1 Case definition for scrub typhus in China

Suspected cases

(1) the individual participated in outdoor activities with possible exposure risk, i.e., farming, fishing, camping, and straw collection, during the disease epidemic season (from May to November south of the Yangtze River and from October to November north of the Yangtze River in China) three weeks before illness onset and presented with fever, lymphadenectasis and skin rash, and diagnosis of other common diseases such as typhus fever, dengue fever or epidemic hemorrhagic fever was excluded;

(2) or the individual had an uncertain exposure history for mite bites but developed fever, lymphadenectasis and skin rash during the local epidemic season of scrub typhus.

Probable cases

(1) the patient is suspected of having the specific eschars/ulcers of scrub typhus;

(2) or the individual participated in an outdoor activity three weeks before illness onset and presented with fever and the specific eschars/ulcers of scrub typhus.

Confirmed cases

(1) a probable case with any of the following four laboratory test results—A) an agglutination titer of ≥1:160 in the Weil-Felix test using the Proteus mirabilis OXK strain; B) a fourfold or greater rise in serum IgG antibody titer (diluted from 1:32 in twofold increments) for mixed antigenic slides (including Karp, Kato, Gilliam and Kawasaki) between acute and convalescent sera, as detected using an indirect immunofluorescence antibody assay (IFA) [11, 13]; C) polymerase chain reaction (PCR) detection of the O. tsutsugamushi 56-kDa gene in clinical specimens; or D) isolation of O. tsutsugamushi from clinical specimens;

(2) or a suspected case with any of the last three abovementioned laboratory test results (B, C or D).