 Current Case
Definition for Surveillance
The clinical case definition is: "Acute onset of
a flaccid paralysis of one or more limbs with decreased
or absent tendon reflexes in the affected limbs, without
other apparent cause, and without sensory or cognitive
loss." Probable cases must meet the clinical case
definition. Confirmed cases must meet the clinical case
definition, and have a neurological deficit 60 days after
onset of initial symptoms, or die, or have unknown follow-up
status. Final classification is made by an expert panel
and only confirmed cases are included in the MMWR. Residual
paralytic disease occurs in approximately 10% of cases
with paralytic illness. Aseptic meningitis occurs in 1%
to 5% of patients with non-paralytic minor illness.
Photo Courtesy of the
World Health Organization
Immunization
The inactivated polio vaccine (IPV) was licensed in 1955
and the trivalent live oral polio vaccine (OPV) in 1963.
Since 1979, IPV has accounted for about 0.1% of all polio
vaccine administered every year in the United States.
After a primary series of three doses of OPV, seroconversion
to all three types is at least 99%. Three properly spaced
doses of OPV have been estimated to have a clinical efficacy
of virtually 100% in a developed country setting and should
confer lifelong immunity.
In Maryland, polio immunization is required by law for
entry into pre-school programs, and kindergarten through
grade twelve. Based on the 1998/99 retrospective kindergarten
survey, an estimated 86% of children in Maryland had received
three doses of OPV by 24 months of age (compared to 85%
in the 1988/89 survey). An all-IPV schedule (all four
doses) is currently being recommended for routine childhood
vaccinations in the United States in order to eliminate
the risk of vaccine-associated paralytic polio. Children
should receive the IPV doses at 2 months of age, 4 months,
between ages 6 and 18 months, and between ages 4 and 6
years.
Historical Trends (see graphs below)
There was substantial fluctuation in the
number of reported cases of paralytic polio in Maryland
from the 1912 to 1960, with a maximum of 481 cases reported
in 1950. Paralysis is more likely when infection occurs
in older individuals. Thus, the appearance of the graph
of the five year mean rates
may be associated with a decline in incidence through
the 1920's related to improvements in sanitation, followed
by an increase in the average age of infection. There
was a steep decline in the five-year mean incidence of
polio in Maryland from the early 1950's through the early
1960's. The last year in which more than two cases were
reported in Maryland was 1961, when 35 cases were reported.
Fifteen cases have been reported since 1961. All six cases
of paralytic polio reported in Maryland since 1977 were
vaccine associated.
Photo Courtesy of the
Centers for Disease Control
Figure
1. Reported Cases of Paralytic Polio in Maryland, 1970-1999.
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