Ombudsman Winnie Chiu on Thursday raised questions over a half-yearly survey done by the Food and Environmental Hygiene Department (FEHD) on rodent infestations in Hong Kong, saying the results could be inaccurate and out of date.

Currently, officials put pieces of uncooked sweet potato, used as "census baits", at 50 different locations for rodent surveillance.

However, Chiu said the methodology should be improved to better gauge the scale of the problem.

"The rate does not reveal the actual number of rodents or the frequency of appearances. In other words, there are limitations on the methodology of survey and as a result the ratio generated may not truly reflect the severity of rodent infestation," she said.

She added that there were serious environmental hygiene problems at some rear lanes, which could lead to rodent infestations.

"During our site visits, we found disposal of articles, refuse, cleansing of utensils and even food preparation being performed at rear lanes."

"FEHD should examine whether the existing mechanism needs improvement to enable more effective monitoring of the cleanliness of shops adjoining rear lanes and explore ways to handle the after-hour cleanliness problems," she added.