West Nile virus (WNV), a mosquito-borne flavivirus introduced recently
to North America, is a human, equine, and avian neuropathogen.1 The
majority of human infections with WNV are mosquito-borne; however, laboratory-acquired
infections with WNV and other arboviruses also occur.2- 4 This
report summarizes two recent cases of WNV infection in laboratory workers
without other known risk factors who acquired infection through percutaneous
inoculation. Laboratory workers handling fluids or tissues known or suspected
to be WNV-infected should minimize their risk for exposure and should report
injuries and illnesses of suspected occupational origin to their supervisor.
Case 1. In August 2002, a microbiologist working in a U.S. laboratory was performing
a necropsy on a blue jay submitted as part of a state's WNV surveillance program.
The microbiologist worked in a Class II laminar flow biosafety cabinet under
biosafety level 2 (BSL-2) conditions5 and
lacerated a thumb while using a scalpel to remove the bird's brain. The wound,
a superficial cut over the dorsal surface of the interphalangeal joint, was
cleansed and bandaged. Four days after injury, the microbiologist had acute
symptoms of headache, myalgias, and malaise followed by chills, sweats, dysesthesias,
recurring hot flashes, swelling of the post-auricular lymph nodes, and anorexia.
Two days later, the microbiologist noted a maculopapular rash that began on
the face; extended to the trunk, arms, and legs during the next 3 days; and
then disappeared gradually. The microbiologist continued to work during illness
and had intermittent chills, sweats, dysesthesias, and hot flashes for approximately
1 week before recovering fully. On the third day of illness (7 days post-injury),
the microbiologist sought medical care from a physician and reported no history
of recent mosquito bites, prolonged outdoor activities, or recent blood transfusion.
On physical examination, the patient was afebrile with erythema on the cheeks,
but the examination was otherwise normal. Serial serum samples taken from
the patient and submitted to CDC for WNV serologic testing revealed evidence
of an acute WNV infection. The initial specimen (collected 3 days after illness
onset) was negative for WNV-specific IgM or neutralizing antibodies. Specimens
collected 13 and 21 days after illness onset both were positive for WNV-specific
IgM antibody; the latter specimen was positive for WNV-specific neutralizing
antibody, with a titer of 160; the specimen collected 13 days after illness
onset was not tested by neutralization. The brain of the blue jay tested positive
at CDC for WNV RNA by real-time polymerase chain reaction (TaqMan®) using
two primer/probe sets.
Case 2. In October 2002, a microbiologist working in a U.S. laboratory who was
harvesting WNV-infected mouse brains in a Class II laminar flow biosafety
cabinet under BSL-3 conditions5 punctured
a finger with a contaminated needle. The wound was cleansed and bandaged.
The microbiologist's body temperature was measured several times each day,
and 3 days after injury, the microbiologist had upper respiratory infection
(URI) symptoms without fever or chills. The next day, URI symptoms continued
with malaise, fatigue, chills, and a low-grade fever (100.9°F [38.3°C]).
That evening, the patient took an over-the-counter cold medication. The next
morning, the patient awoke without fever or chills but with continued URI
symptoms and a dry cough and hoarseness that persisted for >1 week, although
the patient missed only 1 day of work. At no time did the patient notice a
skin rash, an increase in the usual degree of joint pain, or a stiff neck.
The patient reported no history of recent mosquito bites, prolonged outdoor
activities, or recent blood transfusion. The patient had a history of exposure
to multiple flaviviruses or flavivirus antigens (i.e., had had dengue fever
and had received yellow fever and Japanese encephalitis vaccines). Serial
serum samples taken and submitted to CDC for WNV serologic testing revealed
evidence of an acute WNV infection. WNV-specific IgM antibody was absent from
both the initial specimens (1 day after injury and 3 days before fever onset)
and a specimen collected 2 days after fever onset. Anti-flaviviral IgG antibody
was detected in both of these specimens by enzyme-linked immunosorbent assay
(ELISA), but no change in the intensity of IgG activity was observed. A serum
specimen collected 10 days after illness onset was positive for WNV-specific
IgM antibody and showed a sharp increase in the intensity of anti-flaviviral
IgG antibody by ELISA. Neutralizing antibody test results are pending.
G Campbell, MD, R Lanciotti, PhD, Div of Vector-Borne Infectious Diseases,
National Center for Infectious Diseases; B Bernard, MD, H Lu, MD, Div of Surveillance,
Hazard Evaluations and Field Studies, National Institute for Occupational
Safety and Health, CDC.
This report documents two recent laboratory-acquired WNV infections
in the United States. On the basis of the timing of the events described,
WNV infection of the two microbiologists resulted from exposure through percutaneous
inoculation in laboratories. Illnesses in both laboratory workers were mild
and self-limited, which is typical of illnesses in WNV-infected persons.1 These cases confirm that laboratory workers are
at risk for occupationally acquired WNV infection,2- 4 including
West Nile meningoencephalitis.
In the second case, although the presence of heterologous flavivirus
antibodies did not prevent WNV infection, these heterologous antibodies might
have provided some degree of cross-protection that moderated the clinical
severity of the infection. Laboratory workers should not assume that immunity
to other flaviviruses will protect them from WNV infection or its more severe
During the 2002 WNV epidemic and epizootic in the United States,7 the number of laboratories and laboratory workers
involved in arboviral diagnostic and reference activities has increased substantially.
Therefore, the potential for laboratory-acquired WNV infections has increased.
Laboratory-acquired arboviral infections are most likely underreported, and
few recent data are available.3,4 In
2001, a suspected case of laboratory-acquired WNV infection was reported in
New York.8 Laboratory workers involved in
necropsies or other procedures involving materials potentially infected with
WNV should use every precaution to minimize their risk for exposure to fluids
or tissues during handling, including standard droplet and contact precautions;
using and disposing of needles, scalpels, and other sharp instruments safely;
and minimizing the generation of aerosols.
The Subcommittee on Arbovirus Laboratory Safety of the American Committee
on Arthropod-Borne Viruses recommends four biosafety levels for laboratories
that handle arboviruses, comprising combinations of laboratory practices and
techniques, safety equipment, and laboratory facilities.2 Laboratory
investigations that involve handling of live WNV should be conducted under
BSL-3 containment.2,9 However,
because of concerns that strict BSL-3 containment for handling human or animal
specimens in the clinical diagnostic setting would severely limit the number
of laboratories capable of detecting WNV infections in a timely manner, BSL-2
facilities can, with modest modification of their procedures, achieve an acceptable
level of safety for the conduct of certain routine diagnostic procedures involving
live WNV, including bird necropsies.9,10
Participating laboratory employees should receive training that reinforces
awareness of potential occupational hazards and risks and that stresses the
importance of timely reporting of all injuries and illnesses of suspected
occupational origin. After unintentional laboratory incidents of potential
exposure to WNV-infected materials, an exposed person should cleanse any wound
or exposed skin immediately and thoroughly, receive first aid, and then report
the incident to a supervisor, as was done in the two cases described in this
report. No antivirals or other drugs are known to be effective in the prevention
or treatment of WNV infection. A baseline serum specimen should be obtained
and stored. If the worker has an illness within the 2 weeks after the exposure,
prompt medical evaluation, consultation with public health authorities, and
collection of additional serum samples for virologic and serologic analysis
CDC encourages the reporting of all laboratory-acquired arboviral infections
to local, state, and federal public health authorities, regardless of clinical
manifestations. Additional information and consultation about WNV are available
from CDC's Division of Vector-Borne Infectious Diseases, telephone 970-221-6400
or 970-266-3592 or at http://www.cdc.gov/ncidod/dvbid/westnile.
Laboratory-Acquired West Nile Virus Infections—United States, 2002. JAMA. 2003;289(4):414-415. doi:10.1001/jama.289.4.414