Laboratory-Acquired Vaccinia Virus Infection --- Virginia, 2008

Laboratory-Acquired Vaccinia Virus Infection --- Virginia, 2008

Vaccinia virus (VACV) is the live viral component of smallpox vaccine. Inadvertent exposure to VACV can result in infection, and severe complications can occur in persons with underlying risk factors (e.g., pregnancy, immunodeficiencies, or dermatologic conditions) (1). The Advisory Committee on Immunization Practices (ACIP) recommends smallpox vaccination for laboratory workers who handle nonhighly attenuated VACV strains or other orthopoxviruses (e.g., monkeypox, cowpox, or variola) (2). On July 8, 2008, CDC was notified by a Virginia physician of a suspected case of inadvertent autoinoculation and VACV infection in an unvaccinated laboratory worker. This report describes the subsequent investigations conducted by the Virginia Department of Health and CDC to identify the source of infection and any cases of contact transmission. Of the patient's 102 possible contacts, seven had underlying risk factors for developing serious vaccinia infection. Investigators found no evidence of contact transmission and, based on the results of molecular typing, further concluded that the patient had been exposed to a VACV strain that had contaminated the seed stock from the laboratory where the patient worked. This case underscores the importance of adherence to ACIP vaccination recommendations for laboratory workers and use of safety precautions when working with nonhighly attenuated VACV (3).

Case Report

On July 5, 2008, a man in his twenties who worked in a laboratory at an academic institution in Virginia went to a local urgent care clinic. He reported swelling of cervical lymph nodes and pain and inflammation of his right earlobe associated with purulent discharge beginning July 2, followed on July 3 by a feverish feeling and swelling of his left eye with no change in his vision. The patient was prescribed cephalexin for presumed bacterial infection and prednisone for swelling. However, on July 6, his symptoms worsened, and he went to a hospital emergency department. The patient was given bacitracin for his eye and discharged. That night, he noted pustular lesions at similar stages of development on his right ear and left eye (Figure), and also on his chest, shoulder, left arm, and right leg.

On July 7, the patient returned to the emergency department with increasing eye pain and mild photophobia and received a diagnosis of right auricular/pinnal cellulitis and suspected periorbital cellulitis. Prednisone was discontinued, and he was admitted to the hospital for treatment with intravenous vancomycin, ceftriaxone, and pain medications. The same day, an ophthalmology consultation was obtained for left-sided severe preseptal cellulitis, confirmed by computed tomography scan. Biopsy of the conjunctival lesion revealed acute necrotizing conjunctivitis. Slit lamp examination revealed no apparent corneal abrasions and a clear anterior chamber in the left eye, with slight loss of visual acuity. Because the patient's eye infection appeared consistent with keratitis, ceftriaxone was discontinued, vancomycin was continued, and the patient was started on piperacillin/tazobactam and clindamycin.

On July 8, an infectious disease physician who was consulted raised the possibility of suspected VACV infection, among other more common viral or bacterial etiologies, because of histopathologic changes noted in the patient's eye specimens. The consulting physician elicited from the patient that he worked in a cancer research laboratory that handled mice infected with VACV. The physician contacted CDC, which contacted the Virginia Department of Health. Upon further investigation, the patient was determined to have worked with VACV during June 26--28, 4--6 days before symptom onset. This information was inconsistent with the patient's statement during his initial interview on admission the previous day, when he said he recalled last working with VACV in mid-May. Specimens from the patient's eye, ear, arm, and chest were sent to the Virginia Laboratory Response Network. The patient met the CDC surveillance case definition for ocular vaccinia (1).

On July 9, a computed tomography scan revealed worsening of the left preseptal infectious process with intraorbital involvement. On July 10, pending receipt of viral testing, 800 mg acyclovir was administered to the patient intravenously. After receipt of diagnostic testing results, vaccinia immune globulin was not administered because the patient was improving. The patient went on to make a full recovery and returned to his laboratory work in August 2008.

Laboratory Analysis

On July 9, the Virginia Laboratory Response Network tested lesion scrapings from the patient using real-time polymerase chain reaction and detected the presence of nonvariola orthopoxvirus DNA signatures. CDC subsequently confirmed the VACV infection. However, molecular typing of VACV from the patient specimens, performed at CDC, indicated that the patient was infected with a strain (VACV Western Reserve strain) that differed from the VACV strain reportedly used in the laboratory's experiments (the recombinant construct OVA-vac). Because the patient and laboratory VACV strains did not match, investigators had to consider the possibility that the patient might have acquired his VACV infection from another source, most likely within the institution's laboratory complex.

Additional VACV specimens were collected both from the laboratory in which the patient worked and from other laboratories in the academic institution's research complex, and an investigation was launched to identify the source of exposure. CDC analyzed samples of all the virus stocks used at the academic institution and detected a contaminant virus in the OVA-vac stock from the laboratory in which the patient worked that closely resembled the VACV strain isolated from the patient.

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Laboratory-Acquired Vaccinia Virus Infection --- Virginia, 2008