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Subject: Herpes Simplex Virus (HSV) Culture (Rule out)
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HSV infection usually involves vesicular rashes of the oropharyngeal or genital sites, although HSV is capable of causing serious disseminated disease, including infection of multiple organ systems. Vertical transmission may result in neonatal infections, involving localized disease (skin, eyes, and mouth), systemic infection, or encephalitis. Other sites of infection in normal or immunocompromised patients include skin, conjunctiva, and the CNS. HSV can cause severe disseminated disease in immunocompromised patients, resulting in multiorgan dysfunction and failure.
This test may be used to isolate HSV when specific diagnosis is required for patient management.
Patient specimens are inoculated onto cultured eukaryotic cells, like human foreskin fibroblast or Vero cells. Tube or shell vial cultures may be used for HSV isolation. Cytopathic effect is usually manifested within 24–48 hours in specimens with heavy virus loads, such as vesicular lesions.
Specific HSV-1 and HSV-2 antibody reagents may be used to further characterize HSV culture isolates, as needed.
Turnaround time: Most positive cultures are detected within 2 days. Negative tube cultures are typically incubated for up to 7 days. Shell vial cultures are usually finalized within 48–72 hours.
General recommendations for viral culture apply.
Specimens should be collected early in acute infection.
Specimens should be collected according to general recommendations for virus culture of the specimen type. Specimens from cutaneous or mucous membranes are most commonly submitted for viral culture to rule out HSV. Samples should be taken from fresh, wet lesions, ideally from intact vesicles after unroofing.
Most specimens should be placed in a viral transport medium and transported at 4°C.
Positive: Cell cultures positive for HSV indicate probable active infection. Occasionally, positive cultures represent asymptomatic shedding of virus that may be clinically insignificant.
Negative: Negative cell cultures do not rule out HSV infection, especially for CSF and other nonvesicular lesions.
There may be poor sensitivity for certain specimen types, such as CSF. Molecular diagnostic testing may improve detection from these specimens.
Common pitfalls: Collection of specimens from dried, crusted lesions.
HSV-specific DFA, performed on cells from the base of vesicles or wet ulcers, provides rapid and specific identification of HSV infection.
PCR is the most sensitive method for HSV detection and is most useful for diagnosis of CNS infections.
Culture isolates may be typed, but clinical management decisions can generally be made without typing results. Typing is used mainly for epidemiologic purposes.