Epidemic dengue hemorrhagic fever recurred in 1967 on an island in the Gulf of Thailand. All cases seen were categorized by clinical syndrome as shock, hemorrhagic fever, dengue fever, or undifferentiated fever. Paired serum samples were examined for HI, CF, or neutralizing antibody, or both, to dengue, for classification, where possible, into primary or secondary antibody response. There were 68 cases of dengue or probable dengue seen. Among them were five cases of shock syndrome and 10 of hemorrhagic fever; in none of these 15 was there a primary type of antibody response. Dengue virus type 4 was recovered from seven cases in man, while dengue types 1, 2, and 3 had been reported there previously. Cases occurred from mid-July through November; most patients were between 2 and 10 years of age; no sex selection was seen. Areas of the island that had high attack rates in 1966 were relatively spared in 1967, possibly indicating some degree of long-lasting cross-immunity. These observations continue to support the second-infection hypothesis.
Suvit Clinic, Koh Samui, Surat Thani, Thailand.
Alternative address: SEATO Medical Project, U. S. Component, APO San Francisco 96346.