Increased transmission of Zika virus is expected in the U.S. as Aedes mosquitoes emerge in a broad swath across roughly two-thirds of the country as the warmer months come on, raising a critical question for healthcare workers: Can Zika virus be transmitted from an infected patient by a needlestick?

The answer from public health officials is a theoretical, “Yes.”

Though it has yet to be documented, it seems entirely plausible that the stick of a hollow-bore needle containing Zika virus-contaminated blood could simulate transmission via the mosquito’s penetrating proboscis — though the latter is said to probe with an impressive flexibility. Of course, even if Zika is injected into a caregiver via a needle, other variables like the viral titer circulating in the patient’s blood and the immune status of the injured worker would, in part, determine the likelihood of subsequent infection.

“If you consider Zika, it is theoretically possible that a sharps injury or a mucous membrane exposure could transmit the disease,” says David Kuhar, MD, a medical officer in the division of healthcare quality promotion at the CDC. “It remains, of course, possible.”

Indeed, there is every reason to err on the side of caution with blood exposures, given that Zika has already been transmitted sexually, is causing an unprecedented level of birth defects, and is linked to rare cases of Guillain-Barré paralytic syndrome (GBS).

As of April 27, 2016, U.S. public health officials were reporting 426 travel-associated Zika virus disease cases. There were no locally-acquired vector-borne cases, but eight cases were sexually transmitted. Thirty-six of those with Zika were pregnant. There was one case of Zika-related GBS. In contrast, U.S. territories were being heavily hit by local mosquito transmission, with only three of 599 cases related to travel. In addition, 56 pregnant women have been infected and there were five cases of GBS.

“We hope we don’t see widespread local transmission [in the U.S.] but the states need to be ready,” Anne Schuchat, MD, principal deputy director of the CDC, said at a recent press conference. “We have learned that the virus is linked to a broader set of complications in pregnancy — not just microcephaly, but also prematurity, eye problems, and other conditions.”

Puerto Rico is beset with an epidemic, and the situation was expected to worsen before it improves.

“We are quite concerned about Puerto Rico, where the virus is spreading throughout the island,” Schuchat says. “We think there could be hundreds of thousands of cases of Zika virus in Puerto Rico and perhaps hundreds of affected babies.”

While Zika is primarily a public health threat via mosquitoes, the severe birth defects associated with the infection may give pause to healthcare workers who are pregnant or trying to become so, particularly if their patient care duties involve exposure to blood and frequent use of sharps. Though it may provide little comfort, it should be noted that Zika infection progression does not always result in birth defects. Still, in terms of managing risk and avoiding adverse outcomes, it’s hard to imagine a more emotionally charged situation than an expectant nurse balancing work demands against protective maternal instincts.

“Women who work in healthcare have a default to put their patients first, no matter the risk,” says Amber Mitchell, DrPh, MPH, CPH, president and executive director of the International Safety Center (aka EPINet). “The greater spread of Zika and other emerging illness reminds us all that in order to best care for patients, they must put their own safety and wellness on the same plane. Think perhaps, not ‘you first, me next’ – but ‘us together.’”

As employee health professionals are well aware, Zika is just the latest example of bloodborne threats to healthcare workers.

“Since there are dozens of bloodborne pathogens known to cause infection and illness from blood and body fluid exposures like sharps injuries — and more emerging every year — it is more important than ever for healthcare facilities to focus on prevention strategies for sharps injuries, needlesticks, and exposures,” Mitchell says. “Keep track of where exposures are continuing to occur, measure them so that you can target interventions, education, and get better uptake of safety engineered devices.”

Though most Zika cases are asymptomatic, the virus may be present in the blood for approximately one week. That sets up a scenario for transmission via mosquito bites as travelers returning from areas of ongoing transmission serve as reservoirs for subsequent victims of the same mosquitoes. The infection risk is primarily in the community, but the situation warrants vigilance to basic precautions in healthcare as those with the virus in their blood become patients seeking treatment for day-to-day maladies, elective surgery, chronic illnesses, and emergencies.

“There have been no reports yet of transmission of Zika virus to healthcare personnel or other patients,” says Jill Shugart, MSPH, REHS, assistant program coordinator at the National Institute of Occupational Safety and Health (NIOSH). “Minimizing exposures to body fluids is important to reduce the possibility of transmission, but there have not been documented reports as of today [April 27, 2016]. Healthcare personnel should adhere to standard precautions in every healthcare setting – the normal precautions we take to prevent exposures to blood and body fluids that might transmit an infectious agent.”

New Occ health guidelines

A branch of the CDC, NIOSH recently issued Zika occupational health guidelines1 in conjunction with OSHA, reiterating and emphasizing the following exposure control and sharps safety measures for healthcare settings:

  • Follow workplace standard operating procedures (e.g., workplace exposure control plans) and use the engineering controls and work practices available in the workplace to prevent exposure to blood or other potentially infectious materials.
  • Do not bend, recap, or remove contaminated needles or other contaminated sharps. Properly dispose of these items in closeable, puncture-resistant, leakproof, and labeled or color-coded containers.
  • Use sharps with engineered sharps injury protection to avoid injuries.
  • Report all needlesticks, lacerations, and other exposure incidents to supervisors as soon as possible.

Healthcare workers should use standard precautions during patient care regardless of suspected or confirmed Zika infection status, the agencies recommend. However, employers should consider enhanced precautions in situations where workers are at increased risk of exposure to Zika virus or other hazards.

“While there is no evidence of Zika transmission through aerosol exposure, minimizing the aerosolization of blood or body fluids as much as possible during patient care or laboratory tasks may help prevent workers from being exposed to other pathogens,” the guidelines state. Additional protections, including engineering controls to ensure containment of pathogens or enhanced PPE to prevent or reduce exposure, may be necessary during any aerosol-generating procedures or other such tasks, the agencies recommended.

Expect to protect

While currently under revision, the CDC’s 1998 healthcare worker guidelines state that, “Immunologic changes occur during pregnancy, primarily depression of certain aspects of cell-mediated immunity such as decreased levels of helper T cells. These changes permit fetal development without rejection but generally do not increase maternal susceptibility to infectious diseases. … In general, pregnant healthcare personnel do not have an increased risk for acquiring infections in the workplace.” (See related story in this issue.)

The new Zika occupational guidance stresses that healthcare workers understand the risks and routes of exposure and take standard methods to prevent transmission. Workers should be trained to seek medical evaluation if they develop symptoms of Zika. About one out of every five people infected with the virus develops symptoms, usually beginning 2-7 days after the bite of a mosquito carrying the virus. Symptoms are usually mild and can last up to a week. The most common symptoms are fever, rash, joint pain, and red or pink eyes. Other symptoms include muscle pain and headache. These symptoms are similar to those of dengue fever or chikungunya.

Ensure that workers receive prompt and appropriate medical evaluation and follow-up after a suspected exposure to Zika virus, NIOSH and OSHA recommend. If the exposure falls under OSHA’s bloodborne pathogen standard, employers must comply with medical evaluation and follow-up requirements in the standard. Zika is not spread by contact, but it can be spread sexually and safe precautions are advised if either partner has potentially acquired the virus. There are no special measures recommended for pregnant healthcare workers in the new guidelines, though a section on “outdoor workers,” raises the issue of asking for reassignment indoors.

“We wrote this guidance to both employees and employers, and we want to make sure that both groups have the right information,” Shugart says. “Certainly pregnant healthcare workers or anyone who is concerned about Zika should talk to their supervisors. We do recommend that employers train the workers about the risk and working in those environments.”

A separate CDC guideline2 on research laboratory workers states that “the involvement of pregnant workers in studies with Zika virus should be minimized.” For general workers in clinical labs, the CDC recommends that specimens from patients suspected of having Zika virus infection should be handled in accordance with standard precautions that include gloves, a laboratory gown or coat, and eye protection. In general, Biosafety Level 2 precautions are appropriate for the handling of Zika specimens. Laboratories should perform a risk assessment to determine if there are certain procedures or specimens that may require higher levels of biocontainment. For example, potential aerosol-generating procedures should be performed in a biological safety cabinet, the CDC recommends.

In any case, the greatest threat of Zika transmission to pregnant healthcare workers and their colleagues will be in their communities via mosquito bites. Unfortunately, some research with malaria suggests that pregnant women may attract mosquitoes through a slight elevation in body temperature and the exhalation of more carbon dioxide. In a study comparing mosquito attacks on pregnant versus non-pregnant women in Africa, the researchers found those expecting were more likely to be bitten because they exhaled a 21% greater volume of CO2 in the latter stages of pregnancy and their body temperatures were 0.7°C hotter.3

Again, the general tone of public health guidance with Zika is to err on the side of caution. One of the harsh lessons of Ebola was that the virus did not behave in accordance with predictions, forcing the CDC to abandon its initial position that any hospital could handle a case of the virus. Similarly, previous outbreaks of Zika did not herald the explosive association with birth defects seen in the current epidemic in the Americas. A new study4 strongly suggests the reason why: Zika virus has mutated since it was first discovered in Africa in 1947. Sequence analysis of Zika RNA shows the virus “has undergone significant changes in both protein and nucleotide sequences during the past half century,” the researchers report.4 The genetic changes “could play a role in virulence or improved fitness ... and enhanced transmissibility and infectivity from the mosquito vector to the human host,” the researchers concluded.

Zika virus has the potential to spread anywhere that mosquitoes capable of spreading this virus are found, NIOSH warns. Aedes species mosquitoes are the principal vector of Zika virus, particularly Aedes Aegyptus, which is typically concentrated in the southern U.S. as well as parts of the Southwest. Another vector for Zika virus is Aedes albopictus, which are found in much of the southern and eastern part of the U.S. Aedes mosquitoes can also carry other arboviruses, including dengue, yellow fever, chikungunya, Japanese encephalitis, and West Nile.

Another wide-ranging mosquito called Culex has shown the ability to carry the virus in the lab, but not in the wild. Complicating the matter further, a U.K. biotech company is seeking permission to test genetically modified mosquitoes — designed to interrupt the cycle of reproduction — in the Florida Keys. Some residents in the area have taken the position that they are being subjected to a research trial in the absence of informed consent, throwing the proposal into turmoil and delay as this story was filed.

A fascinating modeling study5 recently conducted by the NASA projects that by mid-July, 50 U.S. cities in more than 20 states will be “meteorologically suitable” for Ae aegypti mosquito populations to emerge. (See list in this issue.) In particular, cities in the southeastern U.S. will have conditions suitable for “high abundance” of the mosquitoes, while other eastern cities extending to New York will have “moderate-to-high abundance” and areas out west will be in the low-to-moderate range. The study did not include Ae. albopictus mosquitoes, though there is some concern they could also spread Zika in a less efficient manner.

“This is important because Ae. albopictus has greater cold tolerance than Ae. aegypti, and therefore could facilitate seasonal Zika virus transmission risk in more northerly U.S. cities where Ae. aegypti is not found,” the NASA researchers note.

Indeed, a separate CDC projection6 including Ae. albopictus range expands the possible reach of Zika farther north to include some 30 states up to lower Minnesota in the Midwest and to the lower portion of Maine in the Northeast. Among the many variables are the weather, with the NASA researchers noting projections for June-August 2016 suggest a 40%-45% probability of above-normal temperatures over the entire contiguous U.S. for the upcoming summer of 2016.

“Therefore, it is possible that above-normal temperatures will lead to increased suitability for Ae. aegypti throughout much of the U.S. in summer 2016, though in some of the hottest regions of Texas, Arizona, and California, above-normal temperatures may lead to decreased suitability,” the researchers note.

The NASA study cited socioeconomic factors and poverty as a predictor of human-mosquito exposures, citing factors like lower usage rates of air conditioning, poorer housing infrastructure, and lack of window screens, as well as decreased access to safe water and sanitation.


  1. OSHA, NIOSH. Fact Sheet: Interim Guidance for Protecting Workers from Occupational Exposure to Zika Virus. April 2016:
  2. CDC. Biosafety Guidance for Transportation of Specimens and for Work with Zika Virus in the Laboratory:
  3. Dobson, R. Mosquitoes prefer pregnant women. BMJ 2000; 320:1558.
  4. Wang L, Valderramos SG, Wu A, et al. From Mosquitos to Humans: Genetic Evolution of Zika Virus. Publication stage: In Press. Corrected Proof Cell Host and Microbe. Published Online: April 15, 2016:
  5. Monaghan AJ, Morin CW, Steinhoff DF, et al. On the Seasonal Occurrence and Abundance of the Zika Virus Vector Mosquito Aedes Aegypti in the Contiguous United States. PLOS Curr Outbreaks. March 16, 2016:
  6. CDC. Estimated range of Aedes aegypti and Aedes albopictus in the United States, 2016: