Blood samples collected from 285 residents of South Horizons and nearby Ap Lei Chau following the confirmation of the fifth local Japanese encephalitis case in November show no sign of recent infection with the disease.

The samples came from the five family members of the patient concerned, 257 residents of South Horizons and 23 nearby residents.

The Centre for Health Protection pointed out that blood tests of seven people in the group indicated evidence of past exposure of the disease during their lifetime.

Six of them were born in the endemic areas in Asia, where they probably acquired the infection in the past. The other is a 78-year-old local born woman.

40-year-old patient in serious condition

Overall, the blood tests were consistent with findings of surveys conducted earlier this year. They showed there was a low prevalence of Japanese encephalitis in the Hong Kong population's blood.

No local resident aged below 40 was found to have had previous exposure to the disease in the present survey, compared with 0.3% in the earlier survey.

The fifth patient, a 40-year-old man, developed symptoms on November 1 and was admitted to Queen Mary Hospital on November 5. He is now in serious condition.