RIO DE JANEIRO — Brazil’s government is considering tightening the guidelines it currently gives doctors, hospitals, and health care providers for when to report infants born with abnormally small heads, a move intended to reduce the number of false alarms that it has received in wake of the Zika epidemic gripping Brazil.

In the last few months, the nation has been grappling with a growing surge in medical reports of microcephaly, a rare condition in which babies are born with unusually small heads. According to data released this week by the Ministry of Health, there have been 4,783 reported cases since October last year.

Before that, the nation had about 150 annually.

But how many of the babies actually have microcephaly — and whether the condition was caused by the Zika virus — is still far from clear.

Of the cases examined so far, 404 have been confirmed as having microcephaly.

Only 17 of them tested positive for the Zika virus. But the government and many researchers say that number may be largely irrelevant, because their tests would find the presence of the virus in only a tiny percentage of cases.