Poliomyelitis eradication

Since the poliomyelitis eradication program began in 1988, the number of poliovirus infected continents and countries have decreased from five to two and from greater than 100 to 53, respectively. A nearly 90% reduction in the incidence of polio has been achieved with a corresponding decrease in virus genomic heterogeneity. Major challenges to eradication remain in south Asia and Africa in those areas with hot and humid climates, high population density, and high birth rates. Of particular concern are countries with ongoing social unrest and poor health infrastructure. With the approaching eradication of polio, post-eradication issues are now being addressed. The World Health Organization (WHO) draft plan for containment of wild polioviruses has been published for comment. Commissions and committees for certification of eradication have been established. Still under discussion is the question of the appropriate strategy for stopping oral polio vaccine (OPV) immunization. Studies are underway to determine whether vaccine-derived polioviruses will continue to circulate after OPV cessation and the potential disease consequences of that circulation.

Rehabilitation of the expanded programme on immunization in Sudan following a poliomyelitis outbreak

In 1993 a large outbreak of paralytic poliomyelitis occurred in Sudan as a result of an accumulation of large numbers of susceptible children that was accelerated by faltering immunization services. The extent of the outbreak led to the rapid rehabilitation of Sudan's Expanded Programme on Immunization (EPI); the government began financing vaccine purchase, operational aspects of EPI were decentralized, vaccine delivery was changed from a mobile to a fixed-site strategy, a solar cold chain network was installed, inservice training was resuscitated, and social mobilization was enhanced. National immunization days (NIDs) for poliomyelitis eradication were conducted throughout the country, including the southern states during a cease fire in areas of conflict. Measles immunization coverage was increased by offering measles vaccine during the second round of NIDs and subsequently through routine immunization services. Supplemental tetanus toxoid immunization of women of child-bearing age began in three provinces at high risk for neonatal tetanus. From 1994 to 1996 reported immunization coverage increased and the incidence of all EPI target diseases fell. Trends in coverage, disease incidence, financing, and the implementation of WHO-recommended disease-control strategies suggest that more sustainable immunization services have been re-established in Sudan.

Epidemic cholera in Burundi: patterns of transmission in the Great Rift Valley Lake region

BACKGROUND

After a 14-year hiatus, epidemic cholera swept through Burundi between January and May, 1992. The pattern of transmission was similar to that in 1978, when the seventh pandemic first reached this region. Communities affected were limited to those near Lake Tanganyika and the Rusizi River. The river connects Lake Tanganyika with Lake Kivu to the north in Zaire and Rwanda.

METHODS

To identify sources of infection and risk factors for illness, an epidemiological study was carried out in Rumonge, a lake-shore town where 318 people were admitted to hospital with cholera between April 9 and May 31, 1992. The investigation included a case-control study of 56 case-patients and 112 matched controls.

FINDINGS

Attack rates according to street increased with the street's proximity to Lake Tanganyika (chi 2 test for linear trend, p < 0.01) which suggests that exposure to the lake was a risk factor for illness. Comparison of the 56 case-patients with matched controls showed that bathing in the lake (odds ratio 1.6, attributable risk percentage 37%) and drinking its water (2.78, 14%) were independently and significantly (p < 0.05) linked with illness. No food-borne risk factors were identified. Vibrio cholera 01 was isolated from Lake Tanganyika during, but not after, the outbreak in Rumonge. Isolates from the lake and from patients with acute watery diarrhoea had the same serotype, biotype, and antimicrobial susceptibility profiles. The number of cases rapidly declined when access to the lake was blocked.

INTERPRETATION

This study identifies bathing in contaminated surface water as a major risk factor for cholera in sub-Saharan Africa, and suggests that improving the quality of drinking water alone will have only limited impact on the transmission of the disease in the Great Rift Valley Lake region. The similarity in the patterns of transmission during the 1978 and 1992 epidemics suggests that extensive use of the Great Lakes and connecting rivers for transportation and domestic purposes may be the reason for the explosive cholera outbreaks that occur sporadically in this region.

Overview of poliomyelitis in the African Region and current regional plan of action

The African Region of the World Health Organization includes a diverse membership of 48 countries and territories that has made substantial progress toward controlling poliomyelitis. The coverage with three doses of oral poliovirus vaccine among 1-year-old children reached 58% in 1995, a substantial increase from 49% in 1993, and the incidence of poliomyelitis decreased from 5126 cases in 1980 to 1597 in 1995. To interrupt poliovirus circulation, 29 countries planned to conduct either national immunization days (25 countries) or subnational immunization days (4 countries) during 1996. To ensure the success of these efforts, high-level political commitment has been obtained in many countries, and the campaign to "Kick polio out of Africa" is supported by some of the most respected African politicians. Provided the necessary resources can be obtained from internal and external sources, the African Region may be able to achieve the eradication of poliomyelitis by the year 2000 or shortly thereafter.

The biologic principles of poliovirus eradication

The biologic principles for the global eradication of poliomyelitis are as follows: Poliovirus causes acute, nonpersistent infections, virus is transmitted by infectious humans or their waste, survival of virus in the environment is finite, humans are the only reservoir, and immunization with polio vaccine interrupts virus transmission. These principles appear to be sound. The potential for prolonged virus excretion by immunocompromised patients requires further definition, although there is no epidemiologic evidence of a threat to eradication. Survival of poliovirus in the environment is highly variable, but viral inactivation is usually complete within months. Higher primates may be infected with poliovirus, but they are unlikely reservoirs in nature. The only poliovirus reservoir remaining after eradication will be laboratory stocks. Serious attention must be given to reducing this potential source of infection. Polio eradication through immunization is evidenced by the documented absence of poliomyelitis in an increasing number of countries and the progressive disappearance of poliovirus genotypes.

National immunization days: state of the art

National immunization days (NIDs) are nationwide mass campaigns to deliver supplemental doses of oral poliovirus vaccine to interrupt the circulation of wild polioviruses. They constitute one of the critical strategies for global poliomyelitis eradication and should be implemented in all countries with widespread poliovirus transmission. The certification of wild poliovirus eradication from the Western Hemisphere in September 1994 verified the effectiveness of this aspect of the World Health Organization's (WHO) overall strategy for polio eradication by the year 2000. NIDs require careful advanced planning and orchestration by each country. WHO provides specific guidelines for NIDs regarding the season, target age group, duration, frequency, inclusion of other interventions, vaccine delivery strategies, and evaluation. With strong routine immunization programs and the effective implementation of NIDs, "mop-up" campaigns, and acute flaccid paralysis surveillance, the goal of global polio eradication will be achieved.

Progress toward global polio eradication

Significant progress is being made towards the global eradication of poliomyelitis by the year 2000. The strategies recommended by the World Health Organization for polio eradication are as follows: maintaining high routine immunization coverage; conducting nationwide mass immunization campaigns; building effective, laboratory-based surveillance for acute flaccid paralysis; and conducting localized immunization campaigns directed at the final reservoirs of virus transmission. Sixty-three countries have conducted nationwide anti-polio immunization campaigns. Three hundred million children were immunized in these campaigns worldwide in 1995. The reported incidence of poliomyelitis has fallen by approximately 80% since the global target was set in 1988, and the geographic range of polio is being restricted. The major challenges for achieving eradication are establishing effective surveillance systems in all countries and mobilizing the resources needed to fully implement the recommended strategies in the 67 countries in which polio remains endemic.

Poliomyelitis surveillance: the compass for eradication

Effective disease surveillance is a key strategy of the global polio eradication initiative. In an effort to strengthen the quality of polio surveillance as a prerequisite to achieving and certifying eradication, surveillance assessments were conducted in 28 countries in the World Health Organization African, Eastern Mediterranean, and European Regions from 1992 to 1995 using a standard protocol and evaluation guidelines. Six general recommendations were made: Use surveillance data for public health decision-making and action, improve timeliness of information exchange and dissemination, standardize the data collected, ensure adequate surveillance infrastructure, improve local data analysis, and enhance teamwork among surveillance partners. The experience gained will position the Expanded Programme on Immunization to address the challenges of disease prevention in the 21st century.

A household survey of dysentery in Burundi: implications for the current pandemic in sub-Saharan Africa

To characterize the epidemiology of dysentery (defined as bloody diarrhoea) in Burundi, we reviewed national surveillance data and conducted a household cluster survey including two case--control studies: one at the household, the other at the individual level. We estimated that community incidences for dysentery (per 1000 residents) in Kibuye Sector were 15.3 and 27.3, and that dysentery accounted for 6% and 12% of all deaths, in 1991 and 1992, respectively. Factors associated (P < or = 0.05) with contracting dysentery were being female, using a cloth rag after defecation, a history of recent weight loss, and not washing hands before preparing food. The attributable risk, at the household level, of not washing hands before preparing food was 30%. Secondary household transmission accounted for at most 11% of dysentery cases. This study suggests that Shigella dysenteriae type 1 may be one of the leading causes of preventable mortality in Burundi and other African countries where effective antimicrobial agents are no longer affordable. Since hands were the most important mode of transmission of S. dysenteriae in this study, community-based interventions aimed at increasing hand washing with soap and water, particularly after defecation and before food preparation, may be effective for controlling dysentery epidemics caused by S. dysenteriae type 1 in Africa.