Right now, New York has more cases of Zika virus than any other state: over 200 people have tested positive across the state, with over 150 of those cases in New York City—all contracted abroad. Of those positive tests in the city, 19 were for pregnant women, and nationwide, there are now 234 pregnant women who have tested positive for the mosquito-borne virus, which has been linked to birth defects such as microcephaly. But there may actually be many more women in New York City at risk who have not been tested, many of them low-income or uninsured, the New York Times reports.

Health officials told the Times that much of the testing has been of women from high-income neighborhoods, while women from lower-income neighborhoods who are immigrants from Zika-affected countries in the Caribbean and Latin America are being screened and tested at lower rates.

When the threat of Zika virus in the U.S. became more apparent this winter, the Center for Disease Control recommended that women get tested if the were pregnant or hoped to become pregnant and had recently traveled to a country where mosquitos were transmitting the virus. New York went a step further and said that it would also offer testing to expectant women whose partners had recently traveled to a Zika-affected area, as the virus can be sexually transmitted. All testing in the state is free of cost.

After those guidelines were put in place, 505 pregnant women in the city were tested for the virus, according to the Times. The number of tests performed each month has since dropped: in May, 318 women had reportedly been tested. And there's apparently no way of knowing for sure how many pregnant women may have been infected by the virus, but haven't been tested at all: Dr. Jay Varma, the deputy commissioner for disease control at the city's Department of Health and Mental Hygiene, told the Times that "nobody really keeps data on how many women who traveled to a Zika area should be tested."

Ordering a Zika virus test is time-consuming, the Times reports, and about 70 percent of early samples sent for testing were mislabeled or improperly collected.

An anonymous doctor who works at two hospitals in Brooklyn told the Times that about a quarter of pregnant women visiting those hospitals—hundreds—had traveled to Zika-affected countries recently and were thus eligible for testing, but for months this spring, none were tested at all.

Most people infected with the virus don't show any symptoms, and for people who aren't pregnant or hoping to become pregnant, Zika is relatively benign. But because the virus in a pregnant woman can lead to birth defects—that risk is somewhere between 1 and 29%—testing in that population is of particular importance. It may be especially crucial early on in the pregnancy: a recent study found no woman infected with the virus late in her pregnancy gave birth to a child with birth defects.

In an email to staff at the city's public hospitals, NYC Health & Hospitals President Dr. Ramanathan Raju said that there will soon be an electronic system that will make testing more efficient and easier to initiate, but until then, "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."