A monthly index measuring the presence of aedine mosquitoes shows that two areas – Yau Tong in Kowloon and Wo Che in the New Territories – reached the highest alert level in July with half the surveyed area infested with them.

The monthly index surged to 15.7% in July from 11.3% in June across the city, according to a Food and Environmental Hygiene Department released on Tuesday.

Among 57 surveyed areas, 15 districts under government monitoring reached or exceeded the alert level with a reading above 20%.

As the government added five new districts under monitoring in July – Central and Admiralty on Hong Kong Island, Yau Tong in Kowloon, Wo Che, Tsuen Wan West and Tuen Mun West in the New Territories – they were all reached the warning level.

Yau Tong was the hardest hit area in Hong Kong with a reading of 45.1%, followed by Wo Che with 42.6%. That means almost half of the areas in the two districts were affected by aedine mosquitoes.

Other areas with readings over 20% were Tseung Kwan O North, Kowloon Bay, Kowloon City North, Yuen Kong, Tai Wai, Wong Tai Sin Central, Ma On Shan, Lam Tin, Tsim Sha Tsui and Ngau Chi Wan.

Kwun Tong District councillor Lui Tung-hai slammed the index as it was only announced a month after it was taken, Oriental Daily reported.

Lui urged the department to announce a real-time index to help residents better prepare to prevent or to take control measures against mosquitos. The government said it was studying the proposal to announce the readings in a more timely manner.

Coupled with the 16 confirmed local dengue fever cases recorded so far this month, the FEHD reminded the public to heighten vigilance and keep up effective prevention and control measures against mosquitoes, as well as to take personal protective measures to reduce the risk of contracting mosquito-borne diseases.

Aedes albopictus is a species of mosquito that can transmit dengue fever and the Zika virus.

Read: Mosquito infestation hits alert level in 10 districts