The Health Department recorded 122 new HIV cases in the first three months of this year, the third-highest quarterly figure since 1984, when the first case was found in Hong Kong.
It brought the total recorded number of infections of HIV - the virus that causes Aids - to 5,349.
The tally of new cases was the highest since the third quarter of 2009, when there were 123. In the same period last year, there were only 103 cases. The peak was in the third quarter of 2007, with 125 cases.
The previous quarter, the last three months of last year, saw 121 new cases.
'It is uncommon to have over 120 new cases in two consecutive quarters,' a consultant for the department's special preventive programmes, Dr Wong Ka-hing, said in announcing the figures yesterday. The average was usually about 100.
But he said one reason could be more people having tests for the virus, especially among one of the high-risk groups - men who had sex with other men.
'The number of people going for HIV tests has been on the rise,' Wong said. 'This is a good thing from the point of view of public health.'
Wong said that early diagnosis meant treatment could start earlier, which made it more effective, overseas studies in recent years had shown.
But he said that HIV antibodies, which the test is designed to show, were not produced for about three months after infection, resulting in a negative test result before that.
Men who have sex with men are still the main contributors to new HIV cases, making up 43 per cent of new cases in this year's first quarter. This group accounted for 52 new cases, up from 46 in the same period last year, and about 20 in 2005.
Wong said high-risk groups, which also included sex workers and their clients, intravenous drug users, and spouses or regular partners of HIV-infected people, should have tests every six to 12 months and use condoms.