Brazil's Health Ministry said Wednesday that most of the 508 confirmed cases of microcephaly reported in the country were most likely related to Zika virus outbreak, and it called its previous count too conservative.
Earlier in the day, the ministry reported 4,443 suspected and confirmed cases of the rare defect, up from 4,314 a week earlier. It did not, however, update its total of 41 cases in which it said that microcephaly had been linked by laboratory tests to Zika infections.
Microcephaly is marked by an abnormally small head size that can result in developmental problems. Brazil is investigating a surge in the number of cases across the country in conjunction with the outbreak of Zika, but it has not yet been proved that the virus can cause microcephaly.
To clarify, the ministry said in an emailed statement that the government would cease to update the confirmed number of linked cases because "the Health Ministry considers that there were Zika virus infections in most of the mothers whose babies have been diagnosed" with the condition.
The previous counts, the ministry said, "did not adequately represent the number of cases observed."
Of the total reported Wednesday, Brazil said 508 cases of microcephaly had been confirmed, while 3,935 were still being investigated. Very few of the microcephaly cases can be attributed to causes other than Zika, after extensive analyses and testing, the Health Ministry said.
Zika has proved to be extremely difficult to diagnose. Scientists have been tracking the virus with genetic tests and clinical symptoms.
Zika has now spread to more than 30 countries and has led the World Health Organization to declare a global health emergency.