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

The authorities fumigated neighborhoods 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.

What they did not do was tell the public.

Hardly anyone outside the government knew about the three cases until last week, after the World Health Organization announced that it had received reports about them from the Ministry of Health and Family Welfare. Gujarat state government officials then spoke on May 28 with reporters, saying that there were no more confirmed cases beyond those three.

“The rationale at that time was, if you announce Zika, there might be a bit of panic,” Dr. Soumya Swaminathan, director-general of the Indian Council of Medical Research, a part of the health ministry, said in a telephone interview. “So then there was a decision that there was probably no need for a public announcement at that time.”