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PubMed1991

Sexual contact patterns between men and women and the spread of HIV-1 in urban centres in Africa.

A simple model of the transmission of HIV-1 by heterosexual contact and from mother to unborn infant is developed to assess the influence of patterns of mixing between low and high sexual activity classes of the two sexes on the pattern of spread of the virus and the demographic impact of AIDS. Numerical studies of model behaviour are based, where possible, on parameter estimates derived from epidemiological studies of HIV-1 spread in Africa. Analyses reveal that the assumed pattern of mixing, ranging from assortative (like with like) through random (proportional) to disassortative (like with unlike), has a very major impact on the predicted spread of the virus and the concomitant demographic impact of AIDS. Patterns of strong assortative mixing are predicted to generate the least spread and demographic impact, by comparison with proportional or disassortative mixing. Analyses also reveal that the rules governing behaviour changes, once AIDS-induced mortality changes the structure of the population (i.e. the numbers in the low and high sexual activity classes of the two sexes), have a very significant influence on the course of the epidemic. Where possible, predicted patterns are compared with observed trends in Africa.

Acquired Immunodeficiency Syndrome↗
PubMed1994

A methodology for estimating the contribution of malnutrition to child mortality in developing countries.

According to conventional methods of classifying cause of death, approximately 70% of child deaths (0-4 y) worldwide are due to a small number of priority infectious diseases which, in turn, receive the vast majority of donor and national resources in the health sector. Despite the long-recognized synergism between malnutrition and infection in the causation of child mortality, malnutrition does not appear as a major cause of death in health statistics from developing countries. Part of the reason for this has been the difficulty of estimating the percent of deaths due to malnutrition, because the conventional methods of classifying cause of death do not recognize the potentiating effect of malnutrition on the disease. The purpose of this paper is to develop and test a simple methodology to estimate the percent of child deaths in a given country or community that is due to malnutrition's potentiating effects on prevailing infectious diseases. The cornerstone of the methodology is knowledge of the strength of the association between malnutrition and mortality in developing countries, as measured in eight prospective studies. These studies reveal remarkable consistency in relative risk across different grades of malnutrition. The mean and SE of relative risk for severe malnutrition is 8.4 +/- 2.1, for moderate malnutrition it is 4.6 +/- 0.9, and for mild malnutrition it is 2.5 +/- 0.3. When applied to survey data from Ethiopia, Malawi, Guatemala and India for illustrative purposes, this methodology indicates that 42-57% of all child deaths in these samples (6-59 mo) are due to malnutrition's potentiating effects on infectious disease, of which 76-89% is attributable to mild-to-moderate malnutrition. This methodology is recommended for use in a variety of policy and planning applications.

Child, Preschool↗
PubMed1996

Validation of a method to estimate age-specific human immunodeficiency virus (HIV) incidence rates in developing countries using population-based seroprevalence data.

The authors have conducted an analysis to validate a computer model that uses age-specific human immunodeficiency virus (HIV) prevalence data to estimate age-specific HIV incidence rates. Data for the analysis are from a cohort study of volunteer male workers in Bujumbura, the capital city of Burundi. Testing for HIV prevalence was conducted at baseline, and HIV-negative subjects were retested annually from 1990 to 1993 to determine rates of seroconversion. Input parameters required for the model include age-specific HIV prevalence and estimates of age-specific mortality rates for HIV-negative and HIV-positive subjects. Incidence rate estimates from the model were 2.0, 2.7, 1.0, 1.5, and 1.8 per 100 person-years for age groups 20-24, 25-29, 30-34, 35-39, and 40-44 years, respectively. Corresponding observed incidence rates for the same age groups were 1.6, 1.8, 2.2, 2.3, and 1.5 per 100 person-years, respectively. Most observed incidence rates fell within the 95% confidence limits of the model estimates. Expected numbers of cases within age intervals did not differ significantly from observed number of cases. The authors conclude that the model proved to be successful in approximating observed incidence rates and that it is a useful tool, particularly in countries where prevalence data are available and where HIV prevalence has stabilized, which is when the underlying assumptions in the model are best met. The model provides crucial information about incidence rates that might not be evident from prevalence data alone.

Adolescent↗
PubMed1998

Hyperendemic pulmonary tuberculosis in a Peruvian shantytown.

Estimates of the incidence of pulmonary tuberculosis in developing countries are based on case reporting from local health laboratories or the annual risk of tuberculin skin test conversion. Because these methods are problematic, the authors used a multiple case ascertainment method to estimate the incidence of pulmonary tuberculosis from 1989 to 1993 in a Peruvian shantytown of 34,000 inhabitants. Two methods, face-to-face interview of all local inhabitants and examination of local laboratory smear records, were used for case gathering. The number of missed cases was estimated by capture-recapture analysis. Survey cases with positive smears were matched to age- and sex-matched controls and interviewed about socioeconomic conditions. The average annual incidence per 100,000 population was 364 (95% confidence interval 293-528) by capture-recapture methods. For the city encompassing the shantytown, the Peruvian Ministry of Heath reported an average annual incidence of 134 cases per 100,000 population. The authors conclude that, in Peru, alarming clusters of pulmonary tuberculosis are masked by government reports that pool zones of disparate incidence. Existing estimators of pulmonary tuberculosis incidence based on tuberculin conversion rates may be invalid in such areas. Within these hyperendemic areas, persons suitable for intensive prophylaxis efforts cannot be reliably identified by housing and socioeconomic risk factors.

Adult↗
PubMed1983

Spontaneous abortion and induced abortion: an adjustment for the presence of induced abortion when estimating the rate of spontaneous abortion from cross-sectional studies.

The existence of high rates of induced abortion in the population may distort currently employed measures of the rate of spontaneous abortion. Since the frequency of induced abortion varies greatly between and within populations, an appropriate correction is needed to restore the comparability of spontaneous abortion rates. A simplified estimate of the "true" rate of spontaneous abortion is proposed. This statistic yields a sufficient approximation for most purposes.

Abortion, Induced↗
PubMed1988

The onset of decline in ischemic heart disease mortality in the United States.

Temporal and spatial patterns of the onset of the decline in ischemic heart disease mortality in the United States for each of the 48 contiguous US states and the District of Columbia are examined for the years 1955-1978 for age-sex-race-specific mortality. Mortality rates are derived from National Center for Health Statistics mortality data, and a polynomial interpolation is used to estimate intercensal population counts employing 1950, 1960, 1970, and 1980 US Census data. A quadratic regression equation is used to estimate the date of highest rate, which marks the beginning of the decline for each of the US states. The temporal distribution of the onset of the decline among men occurred primarily between 1960 and 1965. Among women, the onset of decline was more variable. Furthermore, strong and regular spatial patterns were seen among the groups examined and these impressions are supported by statistical analysis. California, Maryland, and the District of Columbia were early decliners in most groups studied, whereas states in the southeast were consistently among the last to experience the onset of decline. These patterns suggest the existence of an underlying phenomenon accounting for the spread or diffusion of the onset of decline in ischemic heart disease mortality.

Adult↗
PubMed1988

Combined effect of childbearing, menstrual events, and body size on age-specific breast cancer risk.

Pike et al. (Nature 1983;303:767-70) and Moolgavkar et al. (JNCI 1980;65:59-69) proposed quantitative theories for the effect on age-specific breast cancer risk of ages at menarche, first childbirth, and menopause. Here the incidence rate functions predicted by these theories are fit to data for 1,884 women of all ages with breast cancer and 3,432 matched controls admitted to San Francisco Bay area hospitals in 1970-1977. A third function describing age-specific breast cancer risk based on the timing of childbearing and menstrual events is presented, and its fit to the data is compared with that of the functions of Pike et al. and Moolgavkar et al. None of the three fully accounted for the protective effects of early age at first childbirth in premenopausal women or of early age at menopause in parous postmenopausal women. To account for the effects of total parity and body mass (Quetelet) index on risk of breast cancer occurrence, the authors developed a fourth incidence rate function by extending the third. Goodness of fit to the data of the fourth function is demonstrated. Age-specific relative risks of breast cancer according to childbearing, menstrual events, and body size are estimated from the fourth function. The main qualitative findings are that 1) the protective effects of late menarche and of early first full-term pregnancy are greater in premenopausal than in postmenopausal women; 2) first full-term pregnancy initially boosts the level of risk, but incidence rates increase with age more slowly thereafter; 3) among the parous, multiparity is protective both in premenopausal and postmenopausal women, regardless of age at first full-term pregnancy; 4) both nulliparous and lean women are more protected by early menopause than are parous and overweight women; 5) increased body mass index is protective before, but detrimental after, menopause; and 6) postmenopausal incidence rates increase with age more rapidly among overweight than among lean women.

Adolescent↗
PubMed1990

Assigning race to occupational cohorts using census block statistics.

Race is an important determinant of disease frequency, yet the race of subjects in retrospective epidemiologic studies is frequently unknown. If addresses are available, the race of study subjects may be estimated from the racial composition of the blocks on which they have resided. Such information can be obtained from census block statistics for Standard Metropolitan Statistical Areas and, with the 1990 Census, probably for the entire United States. The authors assigned black race to persons on blocks with greater than 60% black residents and white race to those residing on blocks containing less than 40% blacks. The validity of the procedure was tested on 341 decedents of known race who resided at the time of death within the Detroit, Michigan, Standard Metropolitan Statistical Area. Thirteen individuals who lived on blocks with 40-60% blacks were excluded from analysis, as well as 18 others for whom racial composition of blocks could not be ascertained. In 293 (94%) of the remaining 310 persons, race assigned on the basis of census information agreed with race obtained from death certificates. This method should prove useful for assigning race to study subjects lacking racial identification.

Black or African American↗
PubMed1992

Epidemic poliomyelitis in The Gambia following the control of poliomyelitis as an endemic disease. II. Clinical efficacy of trivalent oral polio vaccine.

An epidemic of poliomyelitis caused by poliovirus type 1 occurred in The Gambia from May to November 1986. Descriptive findings and vaccination coverage levels are reported in part I. This article (part II) describes a case-control study to estimate the clinical efficacy of three or more doses of trivalent oral polio vaccine compared with zero doses. "Cases" were 1- to 7-year-old children paralyzed during the epidemic who were diagnosed as having poliomyelitis by designated referral physicians. They were identified by reports from referral physicians during the epidemic and by a nationwide village-to-village search after the epidemic. Up to five controls were randomly selected for each case from among children of the same age and sex living in neighboring households. In a matched analysis of 195 cases and 839 controls, the efficacy of three or more doses of trivalent oral polio vaccine was 72% (95% confidence interval 57-82) when children without vaccination cards were considered unvaccinated. The efficacy of three or more doses in 1- to 2-year-old children, in whom the determination of vaccination status was considered to be more accurate than in older children, was 81% (95% confidence interval 66-90). Vaccine failure was not associated with short intervals between doses. Higher levels of vaccination coverage and efficacy than those achieved in The Gambia may be needed in African countries to prevent the return of poliomyelitis as an epidemic disease after it has been controlled as an endemic disease.

Age Factors↗
PubMed1992

Is stroke mortality on the decline in England?

This paper challenges the assumption that mortality from stroke will remain constant or decline over the next few decades. A decline in stroke mortality could be brought about by changes in factors acting close to the time of death (period effect) or by risk factors determined by the generation into which a person is born (cohort effect). Age-specific death rates for stroke (1931-1985) in England and Wales were analyzed to estimate the influence of these different effects. There were significant effects for age, period, and cohort on mortality from stroke with significantly different age and period effects in each sex. The effect of age was linear, with an increasing mortality with age in both sexes. Cohort analysis demonstrated a deceleration away from the previous trend in the mortality rates associated with birth cohorts born after 1880, followed by an acceleration in the trend of mortality rates in cohorts born after 1910. These relative increases in risk for cohorts born after 1910 were offset by a deceleration in mortality associated with periods from around 1951-1954. Since cohort effects are likely to be associated with a lifetime increase in risk of stroke mortality, it is difficult to predict the extent of any long-term fall in stroke incidence.

Adult↗
PubMed1993

Estimation of design effects and diarrhea clustering within households and villages.

The degree to which diarrheal disease clustered within households and within villages among preschool age children was examined using data from four population-based prevalence surveys undertaken in Malawi, Zambia, Indonesia, and Nepal over the past decade. The design effect for each cluster survey was calculated using the diarrhea prevalence, the cluster sizes, and the magnitude of diarrhea clustering within the sampling unit (villages). A recently developed statistical method, alternating logistic regression, was used to estimate disease associations within households of up to nine preschool age children residing within villages of up to 589 such children. Pairwise odds ratios estimating diarrhea clustering within villages ranged from 1.03 (95% confidence interval (CI) 1.01-1.07) in Zambia to 2.19 (95% CI 1.73-2.78) in Indonesia. The design effects ranged from 2.07 (95% CI 1.26-3.19) in Zambia to 7.93 (95% CI 5.16-11.52) in Indonesia. Design effects were strongly dependent on cluster size. The design effects for clusters of size 50 would have ranged from 1.38 to 4.73. Pairwise odds ratios for diarrhea clustering within households ranged from 1.88 (95% CI 1.61-2.19) in Nepal to 10.05 (95% CI 8.46-11.94) in Indonesia. Household odds ratios were always larger than village odds ratios. The village and household pairwise odds ratios adjusted for age, the type of latrine used by the household, and presence of a market in the village were slightly higher than the unadjusted odds ratios. Alternating logistic regression provided useful estimates of disease clustering within villages and household while allowing for covariate adjustment.

Child, Preschool↗
PubMed1995

The AIDS epidemic in India: a new method for estimating current human immunodeficiency virus (HIV) incidence rates.

Human immunodeficiency virus (HIV) incidence rates in India were estimated using a new method that accounts for follow-up bias. Follow-up bias arises in epidemiologic cohort studies when the incidence rate among individuals who do and do not return for follow-up are different. The new method combines data on the prevalence of p24 antigenemia among all those initially screened together with the longitudinal follow-up data on the subset of patients who returned for follow-up. Using these methods, the current HIV incidence rate among patients attending sexually transmitted disease clinics in Pune, India, was 18.6% per year. It was found that follow-up bias can cause significant underestimation in HIV incidence rates, perhaps by as much as 60%. These incidence estimates, together with other HIV seroprevalence studies, suggest the HIV epidemic in India is growing rapidly.

Acquired Immunodeficiency Syndrome↗
PubMed1995

Life expectancy in four U.S. racial/ethnic populations: 1990.

Previous estimates of life expectancy in the United States have not corrected for biases in population and mortality data, and no study has examined life expectancy in U.S. Asian/Pacific Islander and American Indian populations. We used information on population undercounts by race/ethnicity in the census and on misclassification of race/ethnicity on death certificates to calculate life expectancy for black, white, American Indian, and Asian men and women in the United States in 1990. Correction for undercount and misclassification had little effect on life expectancy estimates for whites, but it substantially decreased estimates for American Indians and Asians. Asian men had life expectancies of 82.0 years and Asian women 85.8 years--the highest life expectancies reported for any population in the world and beyond the limit predicted by some current theories.

Adolescent↗
PubMed1990

Transition dynamics of HIV disease in a cohort of African prostitutes: a Markov model approach.

The progression of HIV-related disease from infection to death is represented as a staged Markov model. Transitions between stages are considered reversible. The model is fitted to data from a cohort of African prostitutes by means of maximum likelihood. It appears that the progression to symptomatic disease (Centers for Disease Control stage IV) in this population is considerably more rapid than that reported from studies in Western countries.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Estimating the incubation period of paediatric AIDS in Rwanda.

OBJECTIVE: To estimate the distribution of the incubation period of paediatric AIDS in Rwanda. DESIGN: Data were collected between February 1984 and December 1990 at the Centre Hospitalier de Kigali (CHK), the capital city of Rwanda, Central Africa. PATIENTS: We used a sample of 685 AIDS cases registered consecutively in the Department of Paediatrics of the CHK, in which the proportion of perinatally acquired HIV-1 infection was estimated to be 98.6%. METHODS: We performed both non-parametric and parametric analyses. The methods of estimation were adapted to truncated data, using essentially the same methods as Auger et al. in their analysis of data from the New York City and the New York State AIDS case registries in 1988. RESULTS: We found that a double Weibull model fitted the data very well and that the risk of developing AIDS was high for subjects under 18 months of age, but lower for older subjects. CONCLUSIONS: Our results were qualitatively similar to those of Auger et al.. There were quantitative differences between the two studies, but it was not possible to compare median survival periods. Parameters such as median or mean survival times cannot be validly estimated using only data from registers because these data exclude infected subjects who have not yet developed AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Estimating the seroincidence of HIV-1 in the general adult population in Kigali, Rwanda.

OBJECTIVE: To estimate the seroincidence of HIV-1 infection in the general adult population of Kigali, Rwanda. DESIGN: Repeated standardized cross-sectional studies. SETTING: Two urban prenatal clinics. PATIENTS: A total of 4486 consecutive pregnant women consulting in 1989 and 1990. MAIN OUTCOME MEASURES: Prevalence of HIV-1 antibodies. RESULTS: HIV seropositivity increased by 3-5% annually over this period, indicating that it has not reached a plateau in this sentinel population. The percentage infection rates, calculated using two complementary methods, were 26.2-30.7% in 1990. Extrapolating these results to the general population of Kigali, we estimate that 2300-3800 new infections in young women and 3600-6100 new infections in young men occur annually among the total population of 350,000 in Kigali. CONCLUSIONS: A new HIV infection occurred in an adult every 50-90 min, on average, in Kigali during 1989-1990, while every 6-7 h a baby with maternally acquired HIV infection was born. Our HIV surveillance system, which is based on prenatal sentinel posts, is a useful tool for monitoring the progression of the HIV epidemic in Kigali.

Cross-Sectional Studies↗