Four cases of dengue fever were reported on Tuesday, the highest number the Center for Health Protection has seen in a single day.

However, the controller of the Centre for Health Protection, Dr Wong Ka-hing, said Hong Kong Island had not seen many locally contracted cases of the disease, Radion Television Hong Kong reported.

“In the past few years we had a few cases – it ranges from one to four cases per year in the last few years. The most important thing is we have to be cautious of an outbreak,” Dr Wong said.

Among recent cases were a 17-year-old boy and three elderly people with chronic diseases who were diagnosed between August 2 and 8. Two of those cases were in Kwai Tsing in the New Territories, one in Kowloon’s Wong Tai Sin and the other on the outlying island of Cheung Chau, Sing Tao Daily reported.

The boy lives in Highland Park in Lai King of Kwai Tsing district and played baseball at the Sai Tso Wan Recreation Ground pitch in Kowloon’s Lam Tin nearly every day during the incubation period. He had not travelled abroad in recent weeks.

He developed a fever on Aug. 7 and went to Precious Blood Hospital’s outpatient clinic the following day. On Aug. 12, he was admitted to the Baptist Hospital where he was in a stable condition.

The three elderly patients included a 76-year-old woman who lives in Tsui Chuk Garden in Wong Tai Sin and hikes in the Lion Rock country park every day, a 78-year-old man who lives in Kwai Shing West Estate and an 84-year-old woman who lives on Cheung Chau.

Officers of the Food and Environmental Hygiene Department will visit the affected areas to carry out pest control starting on Wednesday.

Read: Mosquito infestation hits alert level in 10 districts