As the Zika virus swept north from Brazil into the Caribbean, bringing with it frightening risks for pregnant women and their unborn children, United States health officials decided in February that all expectant women who had visited the countries affected should be tested for the disease.

But after the guidelines were put in place, public health officials and doctors in New York City found that large numbers of women, many uninsured or low-income immigrants from the Caribbean and Latin America, were not being screened and tested in a systematic way.

The problems facing the city’s health care providers in ensuring that all of those who need testing can get it illustrates the monumental challenges involved in reaching those considered most at risk. And as summer approaches, the reach of mosquitoes that carry the virus is expected to extend to Florida and other states along the Gulf of Mexico.

The exact number of people missed is not known, because “nobody really keeps data on how many women who traveled to a Zika area should be tested,” said Dr. Jay Varma, deputy commissioner for disease control at the New York City Department of Health and Mental Hygiene.

But officials found that a disproportionate number of those tested were from higher-income neighborhoods, compared with a smaller figure for lower-income neighborhoods with large populations of immigrants from Zika-associated places, Dr. Varma said.

In February, after the new guidelines were put in place, 1,166 tests were performed in the city, 505 of them on pregnant women. But even as awareness grew about the virus and its ties to microcephaly, abnormally small heads and brain damage in infants of infected mothers, the number of tests performed fell: In March, 233 pregnant women were tested, and by May that number had edged up to only 318.

The reasons for that lag are complicated, officials said, and include the absence of an effective commercial test, the resistance of doctors to performing the tests when they deem the risk minimal and a lack of resources for overwhelmed public hospitals and clinics.

One of the biggest stumbling blocks arose from an effort to fix another problem: Some 70 percent of early samples sent to public health labs for testing were rendered useless, because they were mislabeled or improperly collected or handled. Doctors, therefore, were required to telephone the health department for every sample that they wanted to submit, according to Dr. Mary T. Bassett, the city health commissioner.

And ordering a single Zika test in New York City requires a call that lasts, on average, 13 minutes, health officials said.

The average visit to an obstetrician/gynecologist lasts only six to 15 minutes, according to studies, and the requirement set off an immediate backlash, especially in places that were already strained for resources, and where doctors felt they could not handle the burden.

One doctor, who spoke on the condition of anonymity, in part, he said, because of patient confidentiality rules and in part out of fear of repercussions from his hospitals’ management, said that at the two Brooklyn hospitals with which he is affiliated, 20 percent to 25 percent of the pregnant women had a travel history that would make them eligible for testing. This would add up to hundreds of patients.

For several months this spring, virtually none were being tested, he said. His account was backed up by a dozen other doctors and health care experts, who described varying degrees of noncompliance in the testing.

Last week, Dr. Ramanathan Raju, the president of NYC Health & Hospitals, which operates the city’s public hospitals, collectively the largest municipal health care system in the nation, acknowledged the problem in an email sent to the staff.

Dr. Raju wrote that “every provider in our health system has a duty to be vigilant” and follow guidelines from the federal Centers for Disease Control and Prevention and from the city’s health department “to screen for Zika and offer testing when appropriate.”

He said in the email that the city’s public hospitals were working with the health department on an electronic system for initiating the tests.

In the meantime, he warned, “In no way can we allow process issues to prevent us from meeting our responsibility to screen and offer testing in every point of entry to our system — including our emergency departments, ambulatory units and obstetrical settings.”

The health department has offered to pick up all specimens submitted for testing from any practitioner or institution, and Dr. Bassett said the agency had been engaged in increased public outreach. The doctors interviewed said that recently they had seen more attention from their institutions to ensuring that testing took place.

But many doctors and experts said that until testing could be made a part of routine treatment, with a commercial test available, there would be problems.

“We still don’t have timely, specific and efficient tests available; there will not be a vaccine in the foreseeable future; and the public messaging is confusing,” said Dr. Irwin Redlener of Columbia University and its National Center for Disaster Preparedness. “To make matters worse, many health care providers, citing significant bureaucratic challenges, are resistant to making sure that at-risk individuals are screened appropriately. Some cities are struggling to get testing done at all, others are making due with procedures that are still, at best, a work in progress.”

Dr. Bassett said that the problems were not wholly unexpected given that Zika came onto the scene so suddenly, but that testing was crucial not only for the health of the mothers and their babies but also for gaining a better understanding of the virus.

Zika is transmitted by certain species of mosquito and through sex with an infected partner. Eighty percent of those who contract the virus do not show symptoms, so the safest course of action is to get tested.

More people — over 200 — have tested positive for Zika in New York than in any other state. About 150 live in New York City, where tens of thousands of residents have ties to the nations of the Caribbean and Latin America. Of the confirmed cases, 19 involve pregnant women. Nationwide, the number of women infected with Zika during their pregnancies has risen to 234.

There are essentially three tests used to detect the virus; doctors must send three blood and urine specimens from each patient in case multiple tests are needed. The simplest, known as a polymerase chain reaction test, can find traces of the virus in the blood up until about a week after infection, and in urine for about 10 days.

The more complicated test, and the one that can be done only in public labs, looks for antibodies to the virus in the blood, and is supposed to be conducted two to 12 weeks after infection, giving the telltale antibodies time to develop.

However, since Zika is in the same family of viruses as yellow fever and dengue, the tests can provide false positives if a patient has, for instance, been vaccinated for yellow fever. More detailed testing must then be performed.

If an expectant mother tests positive for Zika, there is no treatment, but doctors will perform serial ultrasounds to detect problems in fetal development. Signs of birth defects are not visible until midway through the second trimester at the earliest. Microcephaly has been the most prominent birth defect associated with the disease; scientists are also looking at whether Zika might be associated with other developmental disorders which would not manifest themselves until after birth.

The risk that a woman infected with Zika will pass it on to her fetus, leading to birth defects, is between 1 percent and 29 percent, according to various studies, a number that borders on useless for many practitioners and makes decisions about whether to terminate a pregnancy even more fraught.

Reflecting the urgency of the situation, the World Health Organization recently suggested that millions of women in the affected countries consider delaying pregnancy.

So far, all of the reported cases in the United States have been contracted elsewhere. Experts predict that by the end of the summer, there will most likely be cases of transmission by mosquito in Florida and the Gulf Coast States, further expanding the universe of people who will need testing.

http://www.nytimes.com/2016/06/18/nyregion/zika-testing-lags-in-a-vulnerable-new-york-population.html?_r=1