Chickenpox (varicella) or shingles (zoster) -post-exposure risk assessment: does the person need PEP (post exposure prophylaxis)?
Seek expert advice.
Antivirals are now recommended for post-exposure prophylaxis for all at risk groups apart from susceptible neonates exposed within one week of delivery (either in utero or post-delivery). Varicella zoster immunoglobulin (VZIG) is recommended for those for whom oral antivirals are contraindicated (1,2)
Post exposure prophylaxis is recommended for individuals who fulfil all of the following 3 criteria:
- significant exposure to chickenpox (varicella) or shingles (zoster) during the infectious period
- at increased risk of severe chickenpox such as immunosuppressed individuals,neonates and pregnant women
- no antibodies to varicella-zoster virus (VZV) - urgent VZV antibody testing can beperformed within 24 hours
Definition of a significant exposure to varicella-zoster virus (VZV) - chickenpox or shingles
- three aspects of exposure to VZV during the infectious period are relevant when considering the need for post-exposure prophylaxis (PEP) for a susceptible high risk individual:
- Type of VZV infection in index case:
- PEP should be issued only for those in contact with chickenpox or those in contact with:
- disseminated shingles
- immunocompetent individuals with exposed shingles lesions (for example ophthalmic shingles)
- immunosuppressed individuals with localised shingles on any part of the body inwhom viral shedding may be greater
- the risk of acquiring infection from contact with an immunocompetent individual with non- exposed shingles lesions (for example thoraco-lumbar) is remote and therefore is not an indication for PEP
- Timing of the exposure
- PEP should be offered to contacts in a specified risk group - all immunosuppressed individuals as defined in chapter 6 (Immunisation against infectious disease - the Green Book (5); Annexe 1) are at risk of severe chickenpox and should be assessed for the need for prophylaxis following a significant exposure
- where there is continuous exposure to a case of chickenpox or shingles (see definitions in 'Type of VZV infection in index case' above), for example householdmember, nursery or care worker
- where there has been more than one exposure to a case of chickenpox or shingles(for example family friend who visited on more than one occasion during the infectiousperiod)
- where there has been a single exposure to a case of chickenpox during the infectiousperiod from 24 hours before onset of rash until 5 days after rash appearance inimmunocompetent individuals and until all lesions have crused over forimmunosuppressed individuals
- where there has been a single exposure to a case of shingles (see definitions in 'Typeof VZV infection in index case' above) during the infectious period from onset of rashuntil the lesions have crusted over (in immunocompetent individuals, this is usually 5days after rash appearance)
- Closeness and duration of contact
- in addition to household contacts, the following contacts in the specified risk groups require PEP:
- those in the same small room (for example in a house or classroom or a 2 to 4 bed hospital bay) for a significant period of time (15 minutes or more)
- face to face contact, for example while having a conversation
- immunosuppressed contacts on large open wards, where air-borne transmissionat a distance has occasionally been reported, particularly in paediatric wardswhere the degree of contact may be difficult to define
Period of infectivity of chickenpox or shingles:
- although historically, the infectious period for chickenpox was generally considered as being from 48 hours before, to 4 to 7 days after, onset of rash, a recent review suggested that transmission rarely occurs before the onset of rash, and may continue until all the lesions have crusted over (1)
- in immunocompetent individuals, as a general rule the infectious period the time should be taken as being from 24 hours prior to rash onset to 5 days after rash. For immunosuppressed individuals, it is harder to generalise and therefore the infectious period should be taken from 24 hours prior to rash onset until all lesions have crusted over
- shingles infection is primarily transmitted by direct contact with vesicle fluid in immunocompetent individuals but may be transmitted via infected respiratory secretions from immunosuppressed patients. The infectious period for localised and disseminated shingles is considered as the time from onset of rash until all of the lesions have crusted over
Assessment of susceptibility
- the administration of varicella zoster immunoglobulin (VZIG) is unlikely to confer any additional benefit for patients who already have varicella antibody (VZV IgG) and therefore VZIG is not recommended for individuals with adequate levels of VZV IgG
- assessment of susceptibility will depend on the history of previous infection or vaccination, and the underlying clinical condition
- for immunocompetent individuals including pregnant women, a history of previous chickenpox, shingles or 2 doses of varicella vaccine is sufficient evidence of immunity. In those without such a history, urgent antibody testing should be undertaken on a recent blood sample (booking blood samples are acceptable for pregnant women if available).
- PEP (post exposure prophylaxis) (antivirals or VZIG, if antivirals contraindicated) should be offered if VZV IgG is <100 mIU/ml
- for immunosuppressed patients, a history of previous infection or vaccination is not a reliable history of immunity and VZV antibody levels should be checked urgently
- individuals with VZV antibody levels of 150 mIU/ml or greater are unlikely to benefit from VZIG, and therefore individuals with VZV IgG <150 mIU/ml in a quantitative assay, or negative or equivocal in a qualitative assay should be offered PEP.
- qualitative or quantitative antibody testing is required for all immunosuppressed patients where VZIG is being considered (such as individuals in whom antivirals are contraindicated)
Notes:
- oral aciclovir or valaciclovir are the first choice for post-exposure prophylaxis and should be given from day 7 to day 14 after exposure, but can be started up to 14 days after exposure if necessary
- day of exposure is defined as the date of onset of the rash if the index is a household contact and date of first or only contact if the exposure is on multiple or single occasions respectively (2)
- in individuals with renal impairment or intestinal malabsorption, for example inflammatory bowel disease, VZIG (varicella zoster immunoglobulin) may be considered
- similarly VZIG may also be considered in pregnant women with hyperemesis
- IVIG may be considered in patients considered eligible for VZIG but for whom intramuscular injections are not appropriate.
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