Polio laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
A laboratory diagnosis of poliomyelitis is usually made based on recovery of poliovirus from the stool or pharynx. Neutralizing antibodies to poliovirus can be diagnostic and are generally detected in the blood of infected patients early in the course of infection. Analysis of the patient's cerebrospinal fluid (CSF), which is collected by a lumbar puncture ("spinal tap") reveals an increased number of white blood cells (primarily lymphocytes) and a mildly elevated protein level. Detection of virus from the CSF is diagnostic of paralytic polio, but rarely occurs.
Laboratory Findings
Viral Isolation
Poliovirus may be recovered from the stool or pharynx of a person with poliomyelitis. Isolation of virus from the cerebrospinal fluid (CSF) is diagnostic, but is rarely accomplished. If poliovirus is isolated from a person with acute flaccid paralysis, it must be tested further, using oligonucleotide mapping (fingerprinting) or genomic sequencing, to determine if the virus is “wild type” (that is, the virus that causes polio disease) or vaccine type (virus that could derive from a vaccine strain).
Serology
Neutralizing antibodies appear early and may be at high levels by the time the patient is hospitalized; therefore, a fourfold rise in antibody titer may not be demonstrated.
Cerebrospinal Fluid
In poliovirus infection, the CSF usually contains an increased number of white blood cells (10–200 cells/mm3, primarily lymphocytes) and a mildly elevated protein (40–50 mg/100 mL).
PCR
If poliovirus is isolated from a patient experiencing acute flaccid paralysis it is further tested, using oligonucleotide mapping (genetic fingerprinting), or more recently by PCR amplification, to determine if the virus is “wild type” (that is, the virus encountered in nature) or vaccine type (is derived from a strain of poliovirus used to produce polio vaccine). For each reported case of paralytic polio caused by wild poliovirus, it is estimated that another 200 to 3,000 contagious asymptomatic carriers exist. Therefore, isolation of wild poliovirus constitutes a public health emergency, and appropriate efforts to control the spread of the disease must be initiated immediately.