Figure 1

Figure 1. Images from outbreak of vaccinia virus (VACV) from occupational exposure, China, March 2017. A) Lesion on thumb of case-patient 1; B, C) lesions on hands of case-patient 2; D) batch of...

On March 9, 2017, case-patient 1, an industrial worker, was admitted to a local hospital with high fever and a pustular eruption on his left thumb that appeared 3 days earlier (Figure 1, panel A). Case-patients 2–5 began having fever and skin lesions almost simultaneously and were seen as outpatients at community clinics during March 7–9. Case-patient 1 became ill with severe pneumonia and was transferred to a tertiary hospital for treatment on March 13.

All 5 case-patients worked in a powder processing company. On March 2, they pulverized a batch of frozen skins (Figure 1, panel D) from rabbits inoculated with VACV (Figure 1, panel E) in a biopharmaceutical laboratory 5 days before. Three biopharmaceutical company employees brought the skins to the powder processing company and used the pulverized skins to study the analgesic function of its extracts. The 5 case-patients pulverized the skins in an enclosed workspace (Figure 1, panel G) and did not wear personal protective equipment at any time during the process, which took ≈1 hour. Case-patients 2, 4, and 5 touched the skins with ungloved hands before and after pulverizing. After the pulverizing process, case-patients 3 and 4 disassembled the pulverizer (Figure 1, panel F), and case-patients 1 and 3 washed it with a water cannon. The 3 biopharmaceutical company employees were in the workspace but wore masks and did not participate in the pulverizing process; none became ill or exhibited symptoms.

On March 14, the municipal Center for Disease Control and Prevention initiated an investigation of the 5 febrile case-patients (Appendix Figure). All 5 case-patients were male, 21–53 years of age (Table). Case-patients 1–4 were otherwise healthy and not taking any long-term medications. Case-patient 5 had a history of hypertension; he had fever but no exanthema. Case-patients 3, 4, and 5 reported having a smallpox vaccination in the 1970s; each had a vaccination scar on his left arm. All case-patients had fevers that began 2–5 days after exposure, with high temperatures of 39.0°C–42.0°C. Case-patients 1, 2, and 4 had painful vesicular-pustular lesions on their hands. Case-patient 2 had >7 pustules with a diameter of ≈0.6 cm on each hand (Figure 1, panels B and C). All 5 case-patients had pulmonary infections seen on computed tomography scans on March 20.

Case-patients 2–5 were prescribed antipyretic and antiinflammatory medications, which they took for 9–16 days, and were afebrile 5–9 days after illness onset. They were advised to avoid contact with family members and friends until they were afebrile and escharosis exfoliation was complete. Case 1 was the only patient hospitalized. He was kept in isolation in the tertiary hospital until being discharged on March 24. No transmission occurred from the case-patients to other contacts, and none had scar formation.

Epidemiologic investigation and clinical manifestations raised concerns that cowpox or tularemia were likely etiologies. Nasopharyngeal swab, whole blood, and serum samples were collected from all 5 case-patients on March 14. Clinicians also collected samples of content from scabs from case-patient 1 and liquid from blisters from case-patient 2.

We extracted viral DNA using the QIAamp MinElute Virus Spin Kit (QIAGEN, https://www.qiagen.com). We conducted real-time PCR to screen for OPV (10) and suspected bacteria, including Francisella tularensis and Bacillus anthracis. Case-patients 1–4 tested positive for VACV. All 5 case-patients were negative for cowpox virus, monkeypox virus, F. tularensis, and B. anthracis. We used Hep2 cells (SGST accession no. TCHu 21) to isolate the virus in positive samples, which showed characteristic cytopathic effects, including cell rounding, loss of adherence, and cellular debris 48 hours postinfection.

To establish the relationship between the illness and exposure, we collected residue from the pulverizer blade and outlet and from the surrounding floor. We used real-time PCR to detect VACV-specific nucleic acids in these specimens. We amplified the hemagglutinin gene A56R and sequenced it using an Applied Biosystems 3130 Genetic Analyzer (ThermoFisher Scientific, https://www.thermofisher.com) (11). We aligned nucleotide sequences using ClustalW (http://www.clustal.org/clustal2) and constructed a phylogenetic tree with MEGA5 (https://www.megasoftware.net).

Figure 2

Figure 2. Phylogenetic tree of isolates from outbreak of vaccinia virus from occupational exposure, China, 2017, compared with reference isolates. The tree was constructed by using nucleotide sequences of Orthopoxvirus A56R hemagglutinin genes...

We obtained A56R gene sequences from 5 positive specimens, 1 each from case-patients 1, 2, and 4; 1 from the pulverizer; and 1 from the rabbit skin (GenBank accession nos. MF598168–72). All sequences showed 100% identity match with each other and had 99.6% identity match with isolate VACV-MNR-76 (GenBank accession no. DQ792504) (Figure 2). Unfortunately, we could not trace the vaccine strain used to inoculate the rabbits.

Epidemiologic and molecular data implicated VACV as the etiology of this outbreak, the source of which was rabbit skins inoculated with smallpox vaccine. The phylogenetic tree revealed a close relationship between the isolated strains and the TianTan strain (Figure 2), a highly attenuated VACV strain used in smallpox vaccine in China. The likely transmission route was contact with infected rabbit skins. However, we cannot exclude transmission through aerosolized or suspended infectious particles, considering all 5 case-patients had pulmonary infection and only 3 case-patients had characteristic VACV skin lesions. The transmission mode in this outbreak differs from outbreaks in Brazil and Europe, where human cases were related to contact with infected dairy cattle or to laboratory accidents (12–14).

Case-patients 3, 4, and 5 received prior smallpox vaccination and had less severe clinical manifestations than the other 2 case-patients, indicating that vaccination might have reduced illness severity but failed to protect them from infection (13). Decreased immunity over time and increased virulence of the VACV strain involved might account for the infections.

VACV is commonly used in research settings and the biopharmaceutical industry. Functional studies on extracts from rabbit skins inoculated with VACV are common in China (15). The inadvertent introduction of virulent VACV to local domestic and wild animals could cause a severe outbreak, such as occurred in Brazil (14). Besides using standard contact protections, those who handle animals vaccinated with VACV, or their products, should use proper respiratory protection. In addition, we recommend increased supervision of biopharmaceutical uses of VACV and smallpox vaccination for laboratory and other workers at risk for occupational exposure to OPVs, as recommended in the United States (3).