Notes from the Field: Poliomyelitis Outbreak --- Republic of the Congo, September 2010--February 2011

On November 4, 2010, a case of wild poliovirus type 1 (WPV1) was confirmed in a resident of the port city, Pointe Noire, the first WPV case in Republic of the Congo (ROC) in 10 years. The WPV1 isolate from this resident was genetically most closely related to WPV1 isolated in Angola in 2010. Subsequent investigation, including active case finding, revealed increased acute flaccid paralysis (AFP) hospital admissions beginning in September. Weekly admissions rose from approximately 10 AFP patients in early October to approximately 80 by the end of October and November. With response immunization activities, weekly AFP admissions fell to fewer than five by the end of December. A provisional total of 554 AFP cases were identified nationally, with paralysis onset from September 20, 2010, to February 27, 2011; 374 (68%) of the AFP cases were among males. Overall, 465 (84%) AFP cases were among residents of the neighboring departments of Kouilou and Pointe Noire, where the outbreak apparently began and where approximately 21% of ROC's 4.2 million persons reside. The case-fatality rate (CFR) in Kouilou and Pointe Noire was 40% (187 deaths of 465 cases), compared with 11% (10 of 89) elsewhere in ROC. Additionally, the median age of patients with AFP in Kouilou and Pointe Noire was 20 years (range: 0--63 years), compared with 7.5 years (range: 1--68 years) elsewhere in ROC.

Vaccination status was unknown for all but 149 of the 554 AFP patients. Among those with known vaccination status, 107 (72%) reported having received at least 1 oral polio vaccine (OPV) dose, and 73 of those patients reported receiving at least 3 doses of OPV.

As of March 8, 2011, WPV1 had been confirmed virologically in specimens from 70 AFP patients. Adequate stool specimens were not available for 468 (84%) patients, of whom 190 died; nonetheless, 32 (46%) of the 70 WPV cases were confirmed among those 468 patients. Because investigation of the outbreak was compromised by the collection of adequate specimens from only 16% of patients, the clinical classification algorithm of AFP cases was used. Patients without adequate specimens who died, were lost to follow-up, or had residual paralysis on follow-up were considered to have clinically confirmed polio. This algorithm was applicable when adequate stool specimens were collected for fewer than 65% of cases (4) and was last used in countries of the World Health Organization African Region in 2000. Provisionally, 317 additional patients have been classified as having clinically confirmed polio. Thus, as of March 8, 2011, the total number of confirmed polio cases was 387, pending further laboratory investigation, follow-up, and review.

Outbreak control efforts have included four rounds of national supplementary immunization activities (SIAs) targeting the entire population of ROC, beginning November 12--16 with a round of monovalent type 1 OPV. Subsequent SIA rounds were conducted December 3--7, 2010, using monovalent type 1 OPV; January 11--15, 2011, using bivalent (types 1 and 3) OPV; and February 22--26, 2011, using bivalent OPV. The first three SIA rounds were coordinated with areas of other countries neighboring Kouilou (Cabinda in Angola and Bas-Congo in Democratic Republic of the Congo), where outbreak cases subsequently were reported; the fourth round was synchronized with neighboring Gabon, where a WPV confirmed case occurred in January.

This outbreak appears nearly controlled, with onset of the most recent confirmed WPV case on January 22, 2011. Only 14 AFP cases have been reported provisionally in 2011, approximating the expected background frequency in ROC. Preliminary results suggest that several factors contributed to this outbreak 10 years after the last confirmed WPV1 case in ROC. These include a low rate of childhood polio vaccination among young adults and a protracted period without WPV1 transmission in the area. Vaccination coverage has been low over the last 2 decades,* secondary to weaknesses in the delivery of health-care and routine vaccination services, complicated by civil war and conflict during 1997--1999. The last national SIA was in 2006. Other possible contributing factors are crowding of residents and severe limitations in water supply and sanitation. The high proportion of cases among adolescents and adults (who are known to be at higher risk for bulbar paralysis than children) might have contributed to the high CFR, which might have been accentuated by suboptimal medical care and delays in seeking care. CFRs of 12%--32% have been observed in previous WPV1 outbreaks involving adults (1--3). An investigation is ongoing to determine reasons for the elevated CFR in Kouilou and Pointe Noire.

All international travelers are advised to have completed a primary series of polio vaccinations before travel (5,6). Travelers from the United States to countries with recent WPV transmission or countries neighboring them also should receive a single adult booster inactivated poliovirus vaccine dose before departure.† Travelers who are inadequately vaccinated against polio or whose past vaccination history is uncertain should contact their physician to discuss polio vaccination options before traveling. The World Health Organization recommends that all travelers who reside in countries with WPV transmission not only complete a course of vaccination against polio, preferably with OPV, before leaving the country of residence, but also receive an additional dose of OPV within 12 months before each international trip (6). However, whether many travelers from countries with WPV transmission follow these recommendations, except when required (e.g., pilgrimage to Mecca), is uncertain (7).

Reported by

Ministry of Health, Republic of the Congo; World Health Organization Republic of the Congo Country Office, World Health Organization Regional Office for Africa, Brazzaville; Republic of the Congo. Dept of Polio Eradication, World Health Organization, Geneva, Switzerland. Div of Viral Diseases and Global Immunization Div, National Center for Immunization and Respiratory Diseases, CDC.

References

1. Prevots DR, Ciofi Degli Atti M, Sallabanda A, et al. Outbreak of paralytic poliomyelitis in Albania, 1996. Clin Infect Dis 1998:26;419--25.
2. CDC. Outbreak of poliomyelitis---Cape Verde, 2000. MMWR 2000;49:1070.
3. CDC. Outbreak of polio in adults---Namibia, 2006. MMWR 2006;55:1198--201.
4. World Health Organization. Field guide for supplementary activities aimed at achieving polio eradication. Geneva, Switzerland: World Health Organization; 1997. Available at http://www.who.int/immunization_monitoring/resources/Field_guide_polio_96.pdf. Accessed March 14, 2011.
5. CDC. Travelers' health. Atlanta, GA: US Dept of Health and Human Services, CDC. Available at http://wwwnc.cdc.gov/travel. Accessed March 14, 2011.
6. World Health Organization. International travel and health 2010. Geneva, Switzerland: World Health Organization Press; 2010. Available at http://www.who.int/ith/chapters/en/index.html. Accessed March 14, 2011.
7. World Health Organization. Health conditions for travellers to Saudi Arabia for the pilgrimage to Mecca (Hajj). Wkly Epidemiol Rec 2010;85:425--36.