Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (508 page)

   Laboratory Findings

Viral culture
: Measles virus can be isolated in cell culture from respiratory, nasopharyngeal, conjunctival, blood, or urine specimens.

Pathology/cytology
: Epithelial cells from the respiratory tract, conjunctiva, or urine (early disease), or infected tissues (acute or chronic disease), may be stained to demonstrate multinucleated giant cells with intranuclear and cytoplasmic inclusion bodies.

Serology
: Most infections are diagnosed serologically in the setting of typical clinical findings. See Measles Serology Screen (Measles [Rubeola] IgG and IgM) in Chapter
17
, Infectious Disease Assay.

   Detection of measles virus–specific IgM or a fourfold or greater rise in measles virus–specific IgG in paired acute and convalescent serum specimens are diagnostic.

   IgG antibody levels develop in the week after onset of rash and usually peak in the first month after appearance of the rash. IgM antibodies can usually be detected in the first week of infection and become undetectable after 2 months.

NAAT assays
: May be useful in diagnosis of CNS infection in immunocompromised patients.

SMALLPOX (VARIOLA VIRUS)

   Definition

Smallpox is caused by the variola virus. Historically, smallpox is a highly infectious viral infection associated with significant morbidity and mortality. Humans are the primary natural host for variola virus. An aggressive global vaccination effort eliminated naturally occurring smallpox by 1980. Because the complication rate of smallpox vaccination using the vaccinia virus is relatively high, widespread vaccination is no longer practiced, resulting in a presumed return of widespread susceptibility to this disease. Ominously, laboratory-proliferated variola virus could be weaponized, and this virus is one of the most feared potential bioterror agents. Any patient suspected of having smallpox must be immediately isolated and reported to the relevant Department of Health officials. Case evaluation, management, and diagnostic testing will be directed by state and federal agencies.

   Who Should Be Suspected?

   Smallpox was usually acquired by inhalation of infectious droplets. Spiking fever, headache, and malaise precede the appearance of rash. The typical rash appears about 10 days after exposure and resolves in 4–5 weeks in survivors. The rash progresses from macules to papules to umbilicated pustules. At 2–3 weeks, the host immune response results in scabbing over of pustules and healing of lesions. Scarring, especially on the face, is common in survivors.

   Smallpox is differentiated from chickenpox by the increased toxicity of patients and the pattern of rash. In smallpox, skin lesions appear simultaneously and are more prominent on the face and distal extremities. A rare hemorrhagic form of smallpox was described, most commonly in pregnant women, with a petechial rash, hemorrhage, severe toxicity, and high mortality. Previously vaccinated patients with waning immunity have developed mild disease with few skin lesions that resolved rapidly.

VARICELLA-ZOSTER VIRUS INFECTIONS

   Definition

Varicella-zoster virus (VZV) is the agent responsible for varicella (chickenpox) and zoster (shingles). Chickenpox is the common manifestation of VZV infection, whereas zoster represents a reactivation of latent VZV. VZV may also cause disseminated infection in immunocompromised patients as well as neonatal infections. VZV is a member of the family
Herpesviridae
. There is only one serotype of VZV; all clinical isolates are antigenically related. VZV infections occur worldwide, and most adults in temperate climates have serologic evidence of prior infection even those with no history of chickenpox. Historically, the incidence of chickenpox has been highest in children. Widespread use of varicella vaccine, however, has had an impact on the normal epidemiology with an increasing number of primary infections occurring in young adults.

   Who Should Be Suspected?

   Varicella and zoster are usually relatively mild and self-limited diseases. Morbidity and mortality are low, but more severe disease is often seen in adults, pregnant women, and immunocompromised.