NEW DELHI • Officials in Ahmedabad, India, saw the first case last November: A 34-year-old woman who had just given birth to a healthy child came down with a fever, and tests confirmed she was infected with the mosquito-borne Zika virus.

Officials fumigated neighbourhoods of the city, gathered mosquito larvae for testing, and stepped up their efforts to spot any additional cases, finding two more in the next two months. But what they did not do was tell the public.

Hardly anyone outside the government knew about the cases until last week, after the World Health Organisation (WHO) announced it had received reports about them from the Ministry of Health and Family Welfare. Gujarat state government officials then told reporters last week that there were no more confirmed cases.

The Zika virus attracted global attention in late 2015 when a surge in the number of babies born with microcephaly - abnormally small heads and brain damage - was seen in north-eastern Brazil several months after an epidemic of the mosquito-borne disease in the region. The WHO declared a global health emergency last February. But no cases were reported in India then.

Two of the three people infected in Ahmedabad were women, and both gave birth to healthy babies, said the government. But those were just two out of about 26 million births in India annually. Experts said testing needed to be stepped up.

Across the country, some 40,000 samples have been tested for Zika since last July, and aside from the three reported cases, none had come up positive, said Dr Soumya Swaminathan, director-general of the Indian Council of Medical Research, a part of the health ministry. But those tests would detect recent active infections, not past exposure that could convey immunity.

In addition, 18,000 mosquitoes have been tested, including 500 from the Bapunagar area in Ahmedabad, where two of the Zika cases were reported; those, too, were negative, and officials had not detected any upsurge in microcephaly cases.

NYTIMES