Current status of the global eradication of poliomyelitis.

Substantial progress towards the global eradication of poliomyelitis by the year 2000 has been achieved since May 1988 when WHO Member States adopted this goal at the Forty-first World Health Assembly. Virtually all polio-endemic countries have begun to implement the WHO-recommended strategies to eradicate polio and it is expected that, by the end of 1997, all endemic countries in the world will have conducted full National Immunization Days (NID), providing supplemental oral polio vaccine (OPV) to nearly two-thirds of all children < 5 years. In contrast, although globally acute flaccid paralysis (AFP) surveillance was being conducted in 126 (86%) of 146 countries where polio is or recently was endemic, surveillance remains incomplete and untimely. A global network of polio laboratories, capable of detecting wild poliovirus when and where it occurs, has been developed. Furthermore, in countries where polio virus circulation has been limited to focal areas, and surveillance is adequate, mopping-up campaigns are being conducted to eliminate the final chains of transmission. The process for certification of polio eradication has been established in each WHO region as well as at the global level. The impact of the eradication initiative is evident, with an 88% decrease in the number of reported cases globally since 1988. In order to achieve the goal of eradication, the rapid development of complete and timely AFP surveillance and the continuation of effective NIDs constitute an urgent priority. This is of particular relevance in the remaining polio-endemic countries, especially in those that are affected by war or politically isolated and are important remaining reservoirs from where wild poliovirus continues to spread into bordering or even distant polio-free countries. External support will continue to be required by those countries and regions where the incidence of polio has reached low levels to ensure that final chains of poliovirus transmission are interrupted and to permit the eventual certification of eradication. The year 2000 objective for achieving poliomyelitis eradication remains a feasible target.

HIV infection and breast-feeding: policy implications through a decision analysis model.

OBJECTIVES: (1) To develop a comprehensive decision analysis model to compare mortality associated with HIV transmission from breast-feeding with the mortality from not breast-feeding in different populations and (2) to perform sensitivity analyses to illustrate critical boundaries for guiding research and policy. METHODS: Using a decision tree, mortality rates were estimated for all children, children born to mothers infected during pregnancy, and children born to mothers who were uninfected at delivery. Given various assumptions about child mortality rates, relative risks of mortality among children who are not breast-fed compared with those who are (R), rates of HIV transmission from breast-feeding, HIV prevalence, and HIV incidence, scenarios were created and sensitivity analysis used to delineate critical boundaries. RESULTS: Our model shows that only in situations where R is approximately < or = 1.5 and HIV incidence/prevalence is high (prevalence > 10%, incidence > 5%) would universal breast-feeding result in equal or higher mortality compared with non-breast-feeding. Among populations in many developing countries, where there is a high relative risk of mortality if breast-feeding is not practiced, if R > 3, overall mortality is almost always lower among children who are breast-fed, even by HIV-infected mothers. In situations where maternal HIV status is known, the decision whether to breast-feed is largely dependent on the magnitude of additional mortality risk if the child is not breast-fed. The model illustrates the importance of distinguishing between population and individual recommendations. CONCLUSIONS: Based on available data, the model supports current World Health Organization and Centers for Disease Control recommendations on HIV infection and breast-feeding. Given the importance of breast-feeding and the global impact of HIV infection, more research is needed, especially to clarify the range of HIV transmission rates from breast-feeding and to expand specific assessments of relative risks for different areas of the world.

PIP: HIV/AIDS specialists have developed and applied 3 different scenarios to a comprehensive decision analysis model to estimate mortality rates for children of mothers infected with HIV during pregnancy and for children of mothers who were not infected with HIV during delivery. Scenario I represents Central Africa where HIV prevalence and incidence are high. Some scenario I assumptions are HIV prevalence in pregnant women of 30% and proportion of initially uninfected women who become infected after delivery during lactation (d) of 6%. Scenario II is a population where HIV epidemic is rather recent (e.g., some parts of Asia). Its assumptions are HIV prevalence of 5%, and s is 2%. Scenario III symbolizes high-risk populations in North America and Western Europe (HIV prevalence and s = 1%). The scenarios also consider child mortality rates and relative risks (RRs) of mortality of breast fed children and those who were not breast fed. Universal breast feeding would effect equal or higher mortality than non-breast feeding, when the RR of mortality is no more than 1.5 and HIV prevalence/incidence is high (high prevalence = 10% and high incidence = 5%). In developing countries, where the RR of mortality is high if children are not breast fed (RR 3), breast fed children have almost always lower child mortality than those who are not breast fed, regardless of HIV infection status. The decision to breast feed when the HIV status is known depends greatly on the degree of an additional mortality risk if an infant is not breast fed. The model substantiates WHO and CDC recommendations: HIV-positive women in the UK and the US should not breast feed, while those in developing countries with high RR of child mortality should breast feed. Additional research would define the range of HIV transmission rates from breast feeding and increase specific assessments of RRs for various parts of the world.

The health status of rural primary schoolchildren in Central Zambia.

In a study of 528 rural primary schoolchildren in Central Zambia, it was found that the health status of the schoolchildren was not good as indicated by inadequate nutrition, a high prevalence of S. haematobium (18%), hookworm (33%), and malaria (43%) infections. There were no statistically significant differences in prevalence of undernutrition between girls and boys and there were no significant trends with age. The treatment and control of hookworm disease, urinary schistosomiasis and malaria deserve a high priority in this area. As for malaria, until an international programme on its control can be developed, the acquisition of protective immunity is of paramount importance. This study shows how the use of 'simple' screening procedures can provide information to direct health education and other disease control measures in school health programmes. As the economic situation in Zambia is not good, the best hope for improvement of the children's health lies with environmental improvement in sanitation, water supplies and provision of basic health education.

Prevalence and incidence of HIV infection in Africa: a review of data published in 1990.

PIP: Determination of the prevalence and incidence of HIV infection is essential in monitoring the scope of the HIV pandemic. During the late 1980s, HIV seroprevalence studies and surveys were conducted in most countries in Africa. Despite some problems, seroprevalence studies in many African countries continue to be important advocacy tools for securing or increasing support for HIV/AIDS prevention activities and contribute toward understanding the spread of the pandemic. There have been few studies to determine the incidence of HIV infection in Africa, mainly because of the lack of well-established cohorts, although data on incidence have recently become available. This paper reviews HIV seroprevalence and incidence reports from Africa, published or presented at scientific conferences in 1990, and provides a discussion on the interpretation and use of the data. The prevalence of HIV antibody in Africa is discussed among general population groups, convenience samples of selected groups of individuals, pregnant women attending antenatal clinics, female prostitutes, STD clinic attenders, and hospital patients.^ieng

Epidemiology of human immunodeficiency virus in families in Lusaka, Zambia.

Persons living in the same household as index patients with AIDS or ARC in Lusaka, Zambia were clinically and serologically evaluated for HIV-1 infection. In the 150 households of male index cases, 92 (61.3%) of their spouses were infected, compared with 57 (73.1%) of the spouses of the 78 female index cases. The more advanced the clinical stage of illness in the index cases, the greater the probability of HIV infection in the spouse (RR = 4.44), and the more likely the spouse was symptomatic. Four of the 11 spouses who seroconverted to HIV had also had sexual intercourse at a time when their HIV-infected partner had genital ulcers (RR = 7.45). Of 144 children under 5 years of age, 36 (25.0%) were infected, all had infected mothers and were the last to be borne in all but one household. Three of 120 children 5 to 10 years of age were also infected, presumably through perinatal transmission. Forty-six of 52 discordantly infected couples followed for 1 year continued to have unprotected vaginal intercourse, and 11 (21.2%) of these seroconverted to HIV. There were no HIV infections that could be attributed to transmission by other means than heterosexual intercourse between spouses or by perinatal infection in children borne of infected mothers. The study suggests that there is an increasing risk of HIV heterosexual transmission as infection progresses in the infected partner, and that more effective counseling is needed to prevent it.

PIP: An investigation of members of households of patients with acquired immunodeficiency syndrome (AIDS) and AIDS-related complex (ARC) in Lusaka, Zambia, revealed a high rate of human immunodeficiency virus (HIV) infection in marital partners, regardless of the sex of the index case. The study, conducted in August 1985-June 1987, involved individuals in 244 households of index patients diagnosed with AIDS or ARC. 92 (61.3%) of the 150 male index cases and 57 (73.1%) of the 71 female index cases had an HIV-infected marital partner, and the severity of HIV disease (AIDS or ARC) in the index partner was linearly associated with the severity of HIV disease in the spouse. 10 (25.6%) of 39 uninfected wives of HIV-positive men compared with only 1 (7.7%) of 13 uninfected husbands seroconverted during the 1st year of follow- up. 4 of the 11 spouses who seroconverted during this period reported sexual intercourse at a time when their HIV-infected partner had genital ulcers. Of the 264 children under 10 years of age from 154 households with an HIV-positive adult who were also evaluated as part of this study, 39 (14.8%) were infected--26 had ARC and 13 had asymptomatic infection. Only 3 of the infected children were older than 5 years of age; the mean was 24.9 months. In all cases, transmission in children was attributable to HIV infection in the mother. These findings suggest a need for more aggressive counseling to reduce the sexual transmission of HIV infection to uninfected partners. 46 of 52 discordantly infected couples followed for 1 year continued to have unprotected vaginal intercourse--a factor that certainly contributed to the high concordance of HIV infection among the couples in this study.

The management of diarrhoea in young children in a rural community in Zambia.

Among 64 mothers in two villages in a rural Zambian population who reported childhood diarrhoea, 41 (64%) sought treatment from a health centre or clinic. Among these, 22 (54%) were given oral rehydration salts (ORS) and 19 (46%) were given medications other than ORS. Among the 23 who did not attend a health centre, 14 gave home remedies which included salt and sugar solution, of which, in five, the medicines used were from traditional healers. Overall, 43 (67.2%) of the mothers used some fluids as the first line of treatment. The fluids were infrequently given and in almost all instances, irrespective of the source of the fluid, no more than 15 ml were given over a 24 h period. Furthermore, among the mothers who used fluids, 28 (65.1%) reported stopping the fluids completely if the child vomited. None of the mothers however reported completely withdrawing food from the children. Age and educational level of the mother were not significant factors (P greater than 0.05). These findings suggest that education of mothers on home management of diarrhoea and the proper use of ORS needs to be re-emphasized and health care personnel need to be fully conversant with currently recommended methods for treatment of childhood diarrhoea.

Live or inactivated poliomyelitis vaccine: an analysis of benefits and risks.

Using decision analysis we evaluated the benefits and risks of continued primary reliance on oral poliomyelitis vaccine (OPV) compared to use of inactivated poliovirus vaccine (IPV). We followed a hypothetical cohort of 3.5 million children from birth to age 30 assuming 95 per cent coverage with 98 per cent effective vaccine. Primary reliance on IPV would result in more cases of paralytic poliomyelitis as well as more susceptibles remaining in the population than would be expected with continuing OPV use (74.1 vs 10.0 cases and 5.9 per cent vs 1.1 per cent susceptibles, respectively). However, with OPV use, most cases of paralysis seen would be associated with the vaccine. Our analysis supports a continuation of current US policy placing primary reliance on OPV but the conclusion is heavily dependent on assumptions of risk of exposure to wild virus in the United States. Major declines in risk of exposure to wild virus could alter the balance significantly.

Measles outbreak in a vaccinated school population: epidemiology, chains of transmission and the role of vaccine failures.

An outbreak of measles occurred in a high school with a documented vaccination level of 98 per cent. Nineteen (70 per cent) of the cases were students who had histories of measles vaccination at 12 months of age or older and are therefore considered vaccine failures. Persons who were unimmunized or immunized at less than 12 months of age had substantially higher attack rates compared to those immunized on or after 12 months of age. Vaccine failures among apparently adequately vaccinated individuals were sources of infection for at least 48 per cent of the cases in the outbreak. There was no evidence to suggest that waning immunity was a contributing factor among the vaccine failures. Close contact with cases of measles in the high school, source or provider of vaccine, sharing common activities or classes with cases, and verification of the vaccination history were not significant risk factors in the outbreak. The outbreak subsided spontaneously after four generations of illness in the school and demonstrates that when measles is introduced in a highly vaccinated population, vaccine failures may play some role in transmission but that such transmission is not usually sustained.

Vaccine-associated paralytic poliomyelitis. United States: 1973 through 1984.

From 1973 through 1984, there were 138 cases of paralytic poliomyelitis reported in the United States; 105 (76%) were vaccine associated. Of the 105 vaccine-associated cases, 35 occurred in recipients of oral polio vaccine (OPV), 50 in contacts to OPV recipients, 14 in immune deficient individuals, and six in individuals who had no history of receiving OPV or contact with recent OPV recipients. Thirty-three (94%) of the recipient cases, 41 (82%) of the contact cases, and five (36%) of the immune deficient cases were associated with the first dose of OPV. The overall frequency of vaccine-associated poliomyelitis was one case per 2.6 million doses distributed. However, the relative frequency of paralysis associated with the first dose in the OPV series was one case per 520,000 doses vs one case per 12.3 million subsequent doses. Vaccine-associated paralytic poliomyelitis is rare and the risks of OPV are small. The greatest likelihood of paralysis occurs in association with the first dose of OPV and that likelihood is reduced in subsequent doses more for recipients than for their contacts.

Pertussis epidemic in Oklahoma. Difficulties in preventing transmission.

From Jan 1 to Dec 31, 1983, 351 cases of pertussis were reported in Oklahoma. Overall, 59% of the cases were among children 3 months to 6 years of age, the target age group for pertussis vaccination; only 42% of the patients in this age group were appropriately immunized for age with diphtheria and tetanus toxoids and pertussis vaccine (DTP). A survey of 185 households in the neighborhoods of three cases found that only 65% of 57 children 3 months to 6 years of age were appropriately immunized for their age. Aggressive control of the outbreak was attempted in Oklahoma County with recommendations for widespread vaccination against pertussis. However, the effort failed to immunize 82% of the 931 children in the initial target group. Nonetheless, analysis of the reported cases suggested that less than one fourth of the cases were potentially preventable by a single additional dose of DTP, ie, in individuals 3 months to 6 years of age with a history of at least one prior dose of DTP who were not appropriately immunized for age. The optimal solution to outbreak control is outbreak prevention by ensuring that the maximal number of children younger than 7 years of age receive routine age-appropriate DTP vaccination.

Poliomyelitis in the USA: virtual elimination of disease caused by wild virus.

The average number of paralytic poliomyelitis cases per year in the United States has fallen from 16 000 just before vaccine was introduced in the 1950s to only 12 in 1978-83. 18 of the 69 cases (26%) reported in this 6-year period were not vaccine associated according to the epidemiological classification of paralytic poliomyelitis cases, established in 1975. The van Wezel antigenic differentiation test and oligonucleotide fingerprinting provide a laboratory basis for definitive characterisation of wild and vaccine-like poliovirus strains. Of the 69 cases, isolates from 42 have been analysed; 31 were vaccine-like poliovirus and 11 wild poliovirus. 7 of the wild poliovirus isolates are from cases in a 1979 outbreak caused by poliovirus imported from the Netherlands through Canada; 1 is from a single importation; and 3 are from isolated cases with no identified source. No indigenous wild strain has been isolated from any reported poliomyelitis case since 1981, when a wild strain was isolated from an immunodeficient individual.