MIAMI • Federal health officials have urged pregnant women to stay away from a Miami neighbourhood where they have discovered additional cases of Zika infection - apparently the first time the Centres for Disease Control and Prevention (CDC) has advised people not to travel to a place in the continental United States.
Florida officials said the number of Zika cases caused by local mosquitoes had risen to 14 from the four announced last Friday: 12 men and two women. They declined to say whether either woman was pregnant. All of the cases have been in one neighbourhood.
Health officials said they still did not expect the number of local cases to grow into anything comparable to the epidemic that has raged across Latin America in recent months.
The 10 newly identified patients were most likely infected weeks ago, as early as mid-June, the officials said.
But the new information casts doubt over the effectiveness of mosquito-control efforts in South Florida and elsewhere, after weeks of intensive effort.
Dr Thomas Frieden, the director of the CDC, said that the Aedes aegypti mosquito, which transmits the Zika virus, has proven to be a wily adversary in Wynwood, a crowded, urban neighbourhood in north Miami where the new cases were found.
Aggressive mosquito control measures don't seem to be working as well as we would like.
DR THOMAS FRIEDEN, director of the CDC
The mosquito may be resistant to the insecticides being used or may be able to hide in standing water.
"Aggressive mosquito control measures don't seem to be working as well as we would like," Dr Frieden said in a press briefing on Monday.
The authorities had expected additional cases of Zika infection linked to the neighbourhood, he said. But officials were particularly concerned by indications over the weekend that "moderately high" numbers of Aedes aegypti mosquitoes and their larvae were still being found in a 2.6 sq km section in Wynwood, an area of warehouses, art galleries, restaurants, bars, apartments and condominiums.
"We advise pregnant women to avoid travel to this area," Dr Frieden said, "and pregnant women who live and work in this area and their partners to make every effort to avoid mosquito bites and practise safe sex."
In addition, said Dr Denise Jamieson, a leader of the CDC's pregnancy and birth defects team, "we are recommending women who are considering pregnancy to not get pregnant for up to eight weeks after returning from that area".
No mosquito found in the neighbourhood has tested positive for the virus, but this species has a short life span. Health officials said the Florida mosquitoes carrying the virus had probably acquired it by biting an infected traveller from Latin America or the Caribbean.
In a sign that the Zika cases might affect tourism in Florida, Britain's health agency, saying the risk was moderate, advised pregnant women last Saturday to "consider postponing nonessential travel to affected areas until after the pregnancy".
Mr Jack Ezon, president of Ovation Vacations in New York, said his agency received 22 reservation cancellations on Monday for trips to Florida during the next six months, and that about four times as many people called for information about the travel advisory.
"Yesterday, the news was terrorism. Today, the news is Zika," he said.
NEW YORK TIMES