Scabies
Scabies is caused by an immune reaction to the mite Sarcoptes scabiei var hominis. Other Sarcoptes species and other animal mites, including other variants of S. scabiei, can live but not reproduce on humans; such infestations are self-limiting.
Scabies affect all age and socioeconomic groups and tend to occur in clusters. Outbreaks of scabies are most likely to occur where people live in close proximity in families or in settings where individuals receive personal or health care, such as care homes.
Clinical presentation
The clinical symptoms are severe itching caused by an allergic reaction to a tiny mite that burrows into the top layer of the skin. The skin lesions are evident as papules, vesicles, or small linear burrows containing mites and their eggs. Intense itching occurs mainly at night or after a hot bath or shower. Secondary bacterial infections can occur as a result of scratching.
Typically, scabies lesions can be seen around the finger webs, anterior surfaces of wrists and elbows, anterior axillary folds, belt line and thighs. Nipples, the abdomen, and the lower portion of the buttocks are frequently affected in women, and external genitalia are frequently affected in men. In infants, the head, neck, palms, and soles may be involved; these areas are usually spared in older individuals. The clinical presentation may differ significantly among elderly residents in long-term care settings. Burrows and rashes may affect body parts typically covered by clothing, such as the torso or legs. Some individuals may not complain of symptoms, particularly those with an underlying cognitive impairment who may not be able to communicate their itching or scratching.
Norwegian or crusted scabies is a hyper-infestation with a higher density of mites due to the host’s insufficient immune response. It occurs more commonly in elderly or immunosuppressed patients. The infestation often appears as a generalised dermatitis more widely distributed than the burrows with extensive scaling and sometimes vesiculation and crusting. This form of scabies is highly contagious because the mites multiply rapidly, and large numbers are present in the exfoliated scales.
Incubation period
The allergic reaction does not appear immediately but develops between 2–6 weeks or several months after infection due to a delayed host immune response to the mite. Symptoms may appear earlier (1– 4 days) if the patient has had previous exposure.
Transmission
Human beings are the only source of infection, and infection is spread from person to person through direct skin-to-skin contact, which is usually prolonged and intimate, for example, in a household setting, providing intimate care, or via sexual contact. Casual contact is unlikely to spread the disease unless the affected areas on the patient are heavily excoriated, exposing the mites so they can be easily transmitted.
In healthcare settings, scabies is transmitted primarily through direct contact with an infected person. Hand-holding or patient support for long periods is probably responsible for most healthcare-associated scabies. Transmission to health workers has occurred during activities such as sponge-bathing patients or applying body lotions. Transmission via inanimate objects, such as clothing and bedding, is not common and only occurs if contaminated immediately beforehand, as the mites do not survive for very long out of contact with human skin. Transmission between patients may also be possible when patients are ambulatory. Infection control measures and management of institutional outbreaks of scabies are summarised below.
Prevention and Identification of Outbreaks
- Early recognition of a case is essential to prevent outbreaks. Clinicians should be aware of the potential for asymptomatic infections, particularly in elderly patients.
- An outbreak is defined as two or more epidemiologically linked cases of scabies within eight weeks.
- Strictly implement contact precautions, non-sterile gloves, and long-sleeved single-use disposable gowns for contact with patients/residents.
- Wash hands before and after contact with the patient and after contact with the environment as per the WHO 5 Moments for Hand Hygiene. Hands must be washed after removing gloves.
- Before initiating treatment of single cases, all residents and staff should be checked for symptoms and signs of scabies.
- In the community, if the diagnosis is uncertain, seek advice from a dermatologist, but don’t delay treatment of case or outbreak measures whilst awaiting confirmation.
- In the hospital, inform the IPC team and in the community setting, inform PHA.
Identifying cases and contacts
- Identify all the staff who have provided hands-on care to the patients/roommates before implementing infection control measures.
- Contacts are defined as anyone who has close physical contact with the case without appropriate PPE, for example, providing personal care with skin-to-skin contact, sharing a room or other similar household setting, and having sexual partners within the eight weeks before diagnosis.
- Initiate active case finding, which will include contact tracing of patients and family members who have been in contact with the index case(s)
- Identify new or unsuccessfully treated cases of scabies
- Any agency staff diagnosed with scabies should inform their other places of work, including home (domiciliary) care recipients so that these settings can also be risk assessed and clients identified.
Treatment of cases and contacts
For the clinical management of single cases of scabies, please refer to the NICE guidance.
- Simultaneously treat cases and all exposed individuals to prevent re-exposure and continued transmission.
- Contacts should all be treated at the same time as the index case, on two occasions seven days apart (even if asymptomatic).
- If staff contacts are off duty at the time of treatment, they should complete the first 24-hour treatment dose before returning to work. Refer family members who have been in close physical contact with the patient to their general practitioner so they can be treated if necessary.
- Itching may continue for up to 4 weeks after successful treatment of scabies. Clinical advice should be sought if itching persists for longer than 2–4 weeks after the last treatment application or re-treatment.
Isolation
- Contact precautions and isolation should be implemented for affected patients/care home residents until the first 24-hour treatment for ‘classical’ scabies is completed. Twenty-four hours may not be sufficient for ‘crusted’ scabies because viable mites can persist even after a single treatment. In an institutional outbreak of crusted scabies, it is recommended to isolate the index patient for ten days.
- Healthcare workers can generally return to work the day after treatment and should avoid patient contact for 24 hours after the appropriate treatment is initiated.
- Individuals in the community can return to work, school, or nursery after the first 24-hour treatment is completed, but they should avoid close physical contact during this period.
- It is important to note that ‘crusted scabies’, formerly known as Norwegian scabies, is highly infectious, and transmission can occur through inanimate objects. Therefore, consideration should be given to extending the isolation period in the case of patients who are either heavily infected or immunocompromised.
Other control measures
- Restrict rotation of staff and movement of patients/residents
- Reduce social contact with the confirmed cases by placing restrictions on visitors
- Provide a fact sheet giving information on the spread of scabies and how to prevent it to all relevant staff
- Routine cleaning and disinfection of the environment and vacuuming of the room should be done. The use of insecticide sprays and fumigants is not recommended.
- Fomites should only be handled by staff [including laundry personnel] using personal protective equipment. Sarcoptes scabiei can survive at room temperature for several days in clothing. Therefore, clothing and bedding used anytime during the previous three days before treatment should be machine-washed in hot water and dried thoroughly or ironed. It is important to note that the mites are killed within 10 minutes at a temperature of 50°C. Using hot cycles of both the washer and dryer will kill mites and eggs.
- Clothing and other items that cannot be washed should be treated with insecticidal powder or stored in plastic bags for ten days.
- Continued surveillance is imperative to eradicate scabies in institutions. An outbreak is considered controlled if all the infected individuals are healed and if no new cases of scabies occur in 6–8 weeks after the last patient completes treatment.
References
· NICE: Scabies.London: The National Institute for Health and Care Excellence, July 2023.
https://cks.nice.org.uk/topics/scabies/
- UKHSA guidance on the management of scabies cases and outbreaks in long-term care facilities and other closed settings. (Updated 12 January 2023)
Control of Communicable Diseases Manual (21st ed). Washington: American Public Health Association Press, Jun. 2022.