The fifth case was a female pupil from Hong Bang junior high school in District 5, who tested positive for the bacterium on April 12. She is the sister of a male student who contracted the disease on April 9.

The local medical watchdog called an urgent meeting with the relevant agencies on April 13 to discuss countermeasures.

The results of an epidemiological survey have shown that all these cases of infection are related to food vendors operating near schools, which usually do not meet hygiene requirements.

HCM City has launched a hygiene campaign to raise public awareness of this and to closely monitor people suspected of having the disease.

Vuong Phan Kim, an official from the District 5 People’s Committee, said her district has taken preventive measures such as advising pupils not to eat unhygienic food, spraying disinfectant, improving the quality of canteens and taking samples from food and drinks sold by vendors.