Jpn. J. Infect. Dis., 54, 250-251, 2001@
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Laboratory and Epidemiology Communications
Necessity of Two-Stool Sample Test for Sensitive Detection of Poliovirus
Tetsuo Yoneyama*, Hiromu Yoshida, Kumiko Yoshii, Junko Wada, Hiroyuki Shimizu and Tatsuo Miyamura
Department of Virology II, National Institute of Infectious Diseases, Gakuen 4-7-1, Musashimurayama-shi, Tokyo, 208-0011
Communicated by Tatsuo Miyamura
(Accepted February 4, 2002)
By the initiative of a WHO polio-eradication program, the Western Pacific Region is now declared free of wild poliovirus circulation (1). However, wild polioviruses are still circulating in other restricted areas in the world (2). Consequently, prompt and accurate laboratory diagnosis as well as maintenance of high immunity levels are of critical importance until eradication of poliomyelitis is truly achieved at global level. As a basic strategy, the examination of two stool specimens from one acute flaccid paralysis (AFP) case within 2 weeks has been practiced in the global laboratory network for the program (3). If it were possible to reduce the number of stool collections from two specimens to one without losing diagnostic accuracy, the workload required for laboratory testing and surveillance would be reduced.
Since 1996, stool specimens from AFP patients in Lao People's Democratic Republic (Lao) and Cambodia (Cam) were directly sent to the National Institute of Infectious Diseases in Tokyo and were examined for the presence of polioviruses and non-polio enteroviruses (NPEVs). The last wild poliovirus (type 1) isolate was obtained from a specimen sent from Cambodia in 1997 (4).
We retrospectively analyzed the virus isolation data in our laboratory from 1998 to 2000 and investigated whether the two-stool specimen test actually increased the efficiency of virus detection. NPEVs were isolated by using HEp-2 and RD cell lines, and polioviruses were detected by using the above two cell lines plus L20B cell lines.
Among 772 cases of AFP patients, NPEVs were isolated from 278 cases; 200 cases were detected in both of the two samples, 42 cases in only the first stool sample, and 36 cases in only the second stool sample. The isolation rate (36%) of NPEVs using three different cell lines, HEp-2, RD, and L20B cells far exceeded the WHO requirement (10%) (5). If the number of samples collected had been reduced from two to one, the detection rate of NPEVs would have been reduced from 278 cases to 242 or 236 cases, i.e., by 14%. As for poliovirus isolation, only 65% of the AFP cases (17 cases) were positive in both samples, and 31% of the AFP cases (8 cases) were poliovirus-positive in the second stool specimen only (Table 1). The latter poliovirus could have gone-undetected in the one-stool specimen protocol.
The above data suggest that a substantial number of poliovirus
isolations might have been missed if the second stool specimens
had not been examined. The polio outbreak associated with type
1 circulating vaccine derived poliovirus (cVDPV) in the Caribbean
island of Hispaniola (6) was a quite unexpected, as that polio
outbreak was first thought to be due to a reintroduction of wild
polioviruses from other regions. That outbreak reaffirmed the
importance of maintaining sensitive laboratory poliovirus surveillance
for the possible occurrence of cVDPV as well as wild poliovirus
outbreaks. The two-stool specimen protocol, which significantly
increases the sensitivity of poliovirus detection, should be maintained
until the global eradication of poliomyelitis has been achieved.
The authors thank the laboratory staff in Lao People's Democratic
Republic, Cambodia, and WPRO for arranging the sending of stool
samples.
REFERENCES
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