Smallpox laboratory investigation

Someone either vaccinated previously or vaccinated that day should collect the specimens while wearing a mask and gloves. They should use the blunt edge of a scalpel to open a lesion to obtain vesicular or pustular fluid, a cotton swab to harvest the fluid, and forceps to pick up scabs. They should place the specimens in a 

Clinicians should not order smallpox laboratory testing for moderate or low-risk patients. Given that the global prevalence of smallpox is zero, the positive predictive value of a positive laboratory test for smallpox is extremely low, especially in patients who do not meet the case definition. Testing only high-risk patients for smallpox reduces the likelihood of false positive lab results with their attendant serious consequences. 

Instead, the diagnostic priority for laboratory testing in moderate risk patients is to rule out chickenpox, the disease most commonly confused with smallpox. Therefore, moderate risk patients require rapid diagnostic testing for varicella zoster virus (VZV) (25). 

Several methods are available for rapid detection of VZV in clinical specimens. Although a Tzanck smear is not diagnostic of VZV, most local hospitals with a pathology laboratory can perform the test easily and quickly. A positive Tzanck smear confirms an alphaherpes virus infection, either VZV or HSV (Herpes Simplex Virus). 

Specific tests for VZV include DFA or PCR. DFA uses anti-VZV antibody conjugated to fluorescein dye to detect VZV in cells. Although the DFA is very sensitive and specific, its value is critically dependent on careful specimen collection. PCR of vesicular fluid or scabs can detect VZV DNA directly in 4-6 h. Some local health departments, all state public health laboratories and all large cities contain at least one facility, including private labs and academic health centers, capable of performing rapid diagnostic testing for VZV (25). 

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A survey conducted 20 years ago and based on a total of 3921 cases showed 59% of laboratory-acquired infections had occurred in research laboratories (1). The majority of infections were of laboratory personnel but, in some cases, staff working outside the laboratory were also affected. Other events have emphasized the need for effective biosafety measures. These include two escapes of smallpox virus from laboratories that resulted in members of the public becoming fatally infected the emergence of new viral diseases with high case-fatality rates and the recognition that laboratory-based investigations would need to be made on viruses for which no prophylactic or therapeutic measures were available. Table 1 lists some viruses that have been identified as causal agents of laboratory-acquired infections (2-4). 

On the other hand, the sources and the extent of hazards may be more difficult to assess. There are in effect two sets of raw materials in the workshop the objects being treated, and the materials used to treat them. The object to be treated could present a chemical, biological or mechanical hazard. In some cases, it will be in the laboratory so that more can be learned of its composition or structure. It may, then, be necessary to impute the worst possible hazards to the object until it has been shown to be safe. This is particularly important for some types of biological specimen if there is a history of infection. An example was the archaeological investigation of a graveyard in the City of London in 1985 where it was thought that those interred had died of smallpox. A check was carried out before work started, but no active smallpox was identified. 

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