Companies that employ pregnant women, women who are planning to become pregnant, or even men whose wives or girlfriends are contemplating pregnancy should consider letting them work indoors if they are in areas with Zika transmission, federal health and safety officials said Friday.
If the virus reaches the American mainland this summer the recommendation could impose a major burden on industries such as construction, agriculture, transportation, amusement parks and cafes, which employ hundreds of thousands of outdoor workers.
It was among a general set of guidelines jointly issued by the Centers for Disease Control and Prevention and the Occupational Safety and Health Administration to protect workers from occupational exposure to the Zika virus.
The greatest risk of infection is from mosquito bites, although the new guidelines recognize that the virus can also be transmitted sexually.
As interim guidelines, they are not legally enforceable, said Jordan Barab, the deputy assistant secretary for OSHA at the Labor Department. Issuing advisory guidelines is common during emergencies like epidemics, he said.
The new guidelines also recommended that pregnant employees not travel to areas where the Zika virus is circulating and that businesses consider allowing workers who are or may become pregnant delay traveling to those areas. That recommendation also applies to the male partners of such women.
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The other recommendations made on Friday are based on earlier guidelines issued to protect against West Nile virus. They urge employers to give outdoor workers clothing that covers exposed skin, hats with mosquito netting, insect repellents, and to eliminate standing water near work sites where mosquitoes could lay eggs.
Other guidelines issued Friday covered mosquito-control workers, who face biting insects and hazardous pesticides, and laboratory and health care workers, who could be in danger of acquiring the Zika virus from patients’ blood and bodily fluids.
Mr. Barab said industries that employ outdoor workers had not been consulted before the guidelines were issued.
Jill M. Shugart, an environmental health specialist in the C.D.C.’s National Institute for Occupational Safety and Health, said her organization often consulted with unions and trade groups but in this case had discussed these occupational guidelines primarily with the airline and cruise ship industries.
Those industries were initially concerned with the travel guidelines for pregnant women that the C.D.C. issued in January.
Asked if there had been any reaction from businesses with outdoor employees, she said: “The guidelines were just posted today, and we have not heard from every single sector.”
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Calls to the United States Chamber of Commerce, which represents employers, were not returned Friday afternoon.
It was not clear what constitutes an “area with Zika transmission” for purposes of the workplace guidelines. Mr. Barab said his agency would defer to the C.D.C. on that question.
Ms. Shugart suggested that her agency’s travel guidelines might be used to define such an area, but she added that those parameters are broad.
The agency initially recommended that pregnant women avoid entire countries, then amended that to include only areas below 6,500 feet in elevation because the mosquitoes that carry Zika do not survive at high altitudes.
The only American territories with known Zika transmission are Puerto Rico, the United States Virgin Islands and American Samoa. If the virus reaches Florida or the Gulf Coast this summer, as the C.D.C. has said it might, employers across these regions may not know if their specific location is at risk.
Defining such areas by county or state may be required; presumably, an outbreak in Key West would not affect a job site in Minnesota. Mr. Barab said he assumed that the C.D.C. would eventually come up with a narrower definition.
In the new guidelines, the advice about indoor work is phrased more cautiously than the other guidelines. For example, the new recommendations said that employers should “consider reassigning” employees “if requested by a worker.”