On September 6, 2018, a man with a maculopapular rash, fever, lymphadenopathy, and a 1-week history of feeling generally unwell (patient 2) sought care at a hospital in England (7). He was admitted to a single-occupancy room in the acute medical unit. The staff attending the patient wore standard personal protective equipment (PPE), consisting of disposable aprons and gloves. Because a travel-associated infection was considered possible, patient 2 was transferred to an isolation room on September 7, 2018.

Three days later, a clinical diagnosis of suspected monkeypox was made, and infection prevention and control precautions for a high-consequence infectious disease (HCID) were implemented (e.g., enhanced PPE consisting of disposable gown, disposable gloves, filtering facepiece 3 respirator, and face shield or goggles). The patient was transferred to an Airborne HCID Treatment Centre, and monkeypox was confirmed by laboratory testing at PHE (7).

Although the risk to the public was considered to be very low, a precautionary approach was adopted. Possible hospital and community contacts of patient 2 were identified and assessed for risk (Table). Because smallpox vaccines provide some cross-protection against monkeypox (8,9), a single dose of the third-generation smallpox vaccine, Imvanex (modified vaccinia Ankara; Bavarian Nordic, http://www.bavarian-nordic.com), was offered as postexposure prophylaxis (an off-label indication) to contacts at intermediate and high risk. The target vaccination window for these contacts was within 4 days of exposure, up to a maximum of 14 days from exposure. In addition, preexposure prophylaxis with Imvanex (single dose) was offered to HCID staff involved in the care of confirmed case-patients.

For 3 HCWs who had been assessed for risk, including patient 3 (a healthcare assistant), the same single-exposure risk was identified: >1 episode of close contact with the bedding and clothing of patient 2 before monkeypox was diagnosed. No breaches of standard PPE were identified. All 3 staff members were classified as high-risk contacts and were placed under active surveillance and offered postexposure vaccination. Patient 3 was vaccinated against smallpox on September 14, which was 5 days after the most recent exposure and possibly 6 or 7 days after the earliest exposure to patient 2. Patient 3 had not previously received smallpox vaccine.

On September 22, while off duty, patient 3 noticed a small number of facial lesions and stayed home for the next 2 days but did not report illness to PHE. On September 24, patient 3 sought care with a general practitioner for headache, sore throat, skin lesions on the chin, earache, and eye pain. Patient 3 then reported the illness to PHE.

The general practitioner discussed the case with PHE and provided images of the skin lesions, which were consistent with monkeypox. Further medical assessment of patient 3 at the local hospital was arranged. After assessment and collection of diagnostic specimens, patient 3 remained isolated at home. On September 25, monkeypox was confirmed by PCR testing of multiple sample types, and patient 3 was admitted to an Airborne HCID Treatment Centre.

A total of 134 possible contacts of patient 3 were identified, including staff and patients on the ward where patient 3 worked, family and community contacts, and staff and patients at the general practitioner’s office where patient 3 had sought care. Patient 3 had not been working when rash was present; however, as a precaution, all those who had had contact with patient 3 during the 24 hours before onset of the rash (i.e., on September 21) were monitored. Postexposure vaccination was offered to eligible contacts at intermediate and high risk (Table). As an extra precautionary measure, active monitoring, with daily reporting of presence or absence of signs or symptoms, was extended to all outstanding contacts of patient 2 and all new contacts of patient 3. In addition, HCW contacts at high risk were instructed not to attend work for 21 days from the most recent exposure (the incubation period for monkeypox is 5–21 days) (10).

A total of 4 contacts of patient 3 became ill within the incubation period and required medical assessment. No further cases of monkeypox were identified in relation to this incident and, after clinical improvement, patient 3 was discharged on October 29, 2018.

Cases of human monkeypox outside Africa are rare; in the United Kingdom, the likelihood of travel-associated monkeypox cases is low (10–12). To our knowledge, human-to-human transmission of monkeypox outside Africa has not been reported, and human-to-human transmission of the West African clade has been reported for Nigeria only (4). Such transmission may occur through close contact with skin lesions of an infected person, via fomites, or by exposure to large respiratory droplets during face-to-face contact (1). The transmission reported here occurred from a patient with a travel-associated case to an HCW. The only exposure risk identified during assessment of patient 3 was the changing of potentially contaminated bedding, when patient 2 had multiple skin lesions but before a diagnosis of monkeypox had been considered. The use of standard PPE may not have afforded sufficient protection against monkeypox, particularly if skin lesion debris containing virus had been disturbed and inhaled when bedsheets were changed.

Although patient 3 received postexposure vaccination before symptom onset, vaccination was >4 days after the most recent exposure to patient 2. The optimal timing for postexposure vaccination with Imvanex remains unknown, and the postexposure window period chosen for this incident was informed, in part, by that used during the US outbreak in 2003 (6). Patient 3 may have been vaccinated too late to prevent monkeypox.

During this incident, the risk to the public was determined to be very low because effective human-to-human transmission requires close contact with an infected person or virus-contaminated materials. Regardless, monkeypox is considered an HCID in England because it meets the UK criteria (13).

Monkeypox cases associated with travel to Nigeria have subsequently been detected in Israel (14) and Singapore (15). Although monkeypox is rare outside disease-endemic countries in Africa, this incident illustrates the need to be aware of monkeypox as a reemerging and travel-associated infection. Clinicians should consider a potential diagnosis of monkeypox early for patients with compatible symptoms and potential exposure risks, including recent travel to a disease-endemic country. In healthcare settings, implementation of appropriate infection prevention and control precautions as soon as monkeypox is suspected will help prevent secondary transmission.