Importation of Wild Poliovirus into Qinghai Province - China, 1999

Indigenous wild poliovirus was last isolated in China in 1994. On October 13, 1999, a case of acute flaccid paralysis (AFP) in a 16-month-old boy was reported to public health authorities in Xunhua Autonomous County, Haidong Prefecture, Qinghai Province, China. Following onset of paralysis on October 12, the boy was no longer able to stand or walk. Two stool samples, taken within 14 days of onset of paralysis, were analyzed in the Qinghai provincial laboratory and yielded poliovirus. The isolates were later differentiated as wild poliovirus type 1 at the National Poliovirus Laboratory in Beijing. Stool specimens from one of five children with whom the boy had contact yielded wild poliovirus type 1. This report describes this case of poliomyelitis and the public health response to the case in China.

The case occurred among the Sala, a group of approximately 80,000 persons who live mainly in Xunhua Autonomous County, Qinghai, or in neighboring Gansu province. Many Sala are traders, and Sala men travel widely within Qinghai and to nearby provinces, including Gansu, Sichuan, and Xinjiang, and to Tibet as far south as the border with Nepal. The Sala have trade contacts in India, Pakistan, and Central Asia. Neither the case-patient nor immediate family members are reported to have traveled outside Xunhua County during the 2 months before paralysis onset.

Despite intensive investigations, including retrospective record reviews in health-care facilities and active case searches in villages in selected areas, no additional polio cases or other evidence of continued poliovirus circulation was found. Since 1996, the quality of AFP surveillance in Qinghai has been excellent, with nonpolio AFP rates of greater than 1.5 per 100,000 population and proportion of cases with two adequate stool specimens between 70%-90% annually. The provincial laboratory in Qinghai has shown proficiency in 1999 and received full accreditation within the World Health Organization polio laboratory network.

The Qinghai poliovirus strain is closely related (98%) to poliovirus isolates from central and northern India during 1998-1999, but unrelated to polioviruses that circulated in China until 1994. Despite the absence of a history of travel by the case-patient or his immediate family, evidence suggests that the virus was imported from a neighboring country, probably India, where polio is endemic. The extent of virus circulation following importation has not yet been determined (the paralytic case-to-infection ratio is typically 1:200 in a fully susceptible population). No evidence exists of continued circulation of poliovirus.

Before confirmation of the index case (but after onset of paralysis), provincewide supplementary vaccination with oral poliovirus vaccine, planned earlier in 1999 and targeting children aged 0-3 years, was carried out in late November in both Qinghai and Tibet. In response to confirmation of the index case, an initial local case-response vaccination round was conducted in Xunhua County in November. This was followed by round 1 of a larger, intense house-to-house mopping-up vaccination activity targeting children aged 0-9 years that was implemented in six of eight prefectures of Qinghai, beginning in early December. Round 2 in January 2000 also included house-to-house mopping-up vaccination targeting 7.1 million children in an even larger area, including Qinghai, Ningxia, most of Gansu, and parts of Tibet. These extensive mopping-up vaccination activities were in addition to the second round of subnational immunization days conducted January 5-6, 2000, in all provinces in high-risk areas to vaccinate children aged 0-3 years. All vaccination activities reported good coverage of the target population. Two additional large multiple-province vaccination rounds, targeting approximately 26 million children, are planned for March and April.

Since the case was identified, surveillance activities have been intensified through active case searches in health-care facilities and communities during mopping-up vaccination and retrospective review of hospital records. Special assessments of the quality of virologic surveillance were conducted, including specimen collection and handling procedures, and the quality of specimen processing at the provincial laboratory.

Reported by Ministry of Health; World Health Organization, Beijing, China. Regional Office for the Western Pacific, World Health Organization, Manila, Philippines. Vaccines and Biologicals Dept, World Health Organization, Geneva, Switzerland. Respiratory and Enteric Viruses Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Vaccine Preventable Disease Eradication Div, National Immunization Program, CDC.

Editorial Note:

Preliminary data from this investigation suggest that the polio case in Qinghai was caused by importation of wild poliovirus with limited circulation. No other cases have been detected despite high-quality AFP surveillance and extensive searches of hospital records, health-care facilities, and communities. Further intensive surveillance and vaccination activities, including active house-to-house searches for recent AFP cases, are being conducted.

The detection of this case in a sparsely populated rural area of China indicates that high-quality AFP surveillance continues to be maintained in China. The detection also highlights the need for all polio-free countries to remain vigilant to allow early detection of wild poliovirus imported from countries where polio is endemic and to institute rapid control measures.

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