Epidemiological characteristics of poliomyelitis in Delhi, 1997

To describe the epidemiological characteristics of poliomyelitis in Delhi in 1997 after four consecutive statewide immunization campaigns with oral polio vaccine (OPV).

Stool samples were collected from 158 cases of acute flaccid paralysis (AFP) along with their age, sex, residential address, immunization history and dates of onset of paralysis, reporting and investigation. The samples were processed for isolation of polioviruses. In addition, historical data on vaccination coverage surveys and OPV testing were reviewed. These data were analyzed to understand the epidemiological patterns of poliomyelitis in Delhi.

Of 158 cases of AFP, about 23% were investigated within 2 days of onset of paralysis. Two samples each were collected from 97 (61%) cases, and one each from the remaining cases. Detection of 158 cases of AFP gave an incidence of 1.34 per 100,000 population. About 36% (57/158) of AFP cases excreted poliovirus, mostly (53/158) wild poliovirus. Of the wild poliovirus isolates, 72% (38/53) and 25% (13/53) were serotypes P1 and P3 respectively; 2 isolates were P2. Almost 95% (146/154) of AFP cases and all the laboratory confirmed cases (excreting wild poliovirus) occurred in children below 5 years of age. Only one-third of AFP (55/158) or laboratory confirmed cases (18/53) had received 3 or more doses of OPV before onset of paralysis. About one-fourth of cases in both the categories were totally unvaccinated. AFP cases occurred round the year but peaked in November-December. Peaks were always observed during July-August in the past. The cases were widely scattered without any obvious clustering in any locality.

Poliomyelitis has declined substantially in Delhi. The study underscores the need for further efforts to improve vaccine coverage levels, AFP surveillance, and cold chain maintenance to achieve the complete interruption of transmission.