necrosis (149,150), Ramsay Hunt syndrome (151), aseptic meningitis (152), peripheral motor
neuropathy (152), myelitis (152,153), encephalitis (152), pneumonitis (147), hepatitis (145), and
pancreatitis (142).
The diagnosis of primary varicella infection and herpes zoster is often made clinically.
Diagnosis of the neurological complications can be made with CSF PCR assays (154,155).
Patients with ocular involvement should be seen promptly by an ophthalmologist.
Smallpox
Smallpox is caused by the variola virus. The last known case of naturally acquired smallpox
occurred in Somalia in 1977. The World Health Organization declared that smallpox had been
eradicated from the world in 1980 as a result of global vaccination (156,157). The only known
repositories for this virus are in Russia and the United States. With the threat of bioterrorism,
there is still a remote possibility that this entity would be part of the differential diagnosis of a
vesicular rash.
Smallpox usually spreads by respiratory droplets, but infected clothing or bedding can
also spread disease (158). The incidence of smallpox is highest during the winter and early
spring. The pox virus can survive longer at lower temperatures and low levels of humidity
(159,160).
After a 12-day incubation period, smallpox infection presents with a prodromal phase of
acute onset of fever (often >40 8 C), headaches, and backaches (158). A macular rash develops
and progresses to vesicles and then pustules over one to two weeks (161). The rash appears on
the face, oral mucosa, and arms first but then gradually involves the whole body. The pustules
are 4 to 6 mm in diameter and remain for five to eight days, after which time, they umbilicate
and crust. The lesions of smallpox are generally all in the same stage of development (Fig. 9).
“Pock” marks are seen in 65% to 80% of survivors. Historically, the case mortality rate was 20%
to 50% (158). In the United States, almost nobody under the age of 30 years has been
vaccinated; therefore, this group is largely susceptible to infection.
The diagnosis of smallpox is based on the presence of a characteristic rash that is
centrifugal in distribution. Laboratory confirmation of a smallpox outbreak requires vesicular
or pustular fluid collection by someone who is immunized. Confirmation can quickly be made
Figure 8 Lower abdomen of a patient with a herpes zoster outbreak due to varicella zoster virus.Source:
Courtesy of the CDC, Public Health Image Library.
Fever and Rash in Critical Care 37