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From an analysis of the distributions of measures of transmission rates among hosts, we identify an empirical relationship suggesting that, typically, 20% of the host population contributes at least 80% of the net transmission potential, as measured by the basic reproduction number, [R.sub.0]. This is an example of a statistical pattern known as the 20/80 rule. The rule applies to a variety of disease systems, including vector-borne parasites and sexually transmitted pathogens. The rule implies that control programs targeted at the 'core' 20% group are potentially highly effective and, conversely, that programs that fail to reach all of this group will be much less effective than expected in reducing levels of infection in the population as a whole.

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In 1998, with the launch of the Senegalese Initiative for Antiretroviral Access (ISAARV), Senegal became one of the first African countries to propose an antiretroviral access program. Our objective in this paper is to study the time to any first drug resistance, as well as predictors of the time to resistance. We propose a joint model to study the effect of adherence to the HAART therapy, and virological response on the time to resistance mutations. A logistic mixed model is used to model the time-dependent adherence process; and a Markov model is used to study the virological response. Given the presence of missing data in the adherence process and in the virological response, the latent adherence and virological states are then included in the linear predictor of the time to resistance model. The proposed time to resistance model takes into account interval-censored data as well as null hazard periods, during which the viral replication is very low. A Bayesian approach is used for accommodating with missing data and for prediction. We also propose model checking tools to study model adequacy. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Ebola virus disease (EVD) epidemic that spread in West Africa from the end of 2013 to early 2016 has reached more people than all past epidemics. Beyond care management of acute phase ill patients and measures for the control of the epidemic, the outcome of Ebola survivors became an important question as their number increased and raised new issues. A multidisciplinary prospective cohort of survivors in Guinea has been launched by IRD UMI 233 and Donka National Hospital, Conakry, Guinea, to assess the long-term clinical, psychological, sociological, immunological, and viral outcomes potentially related to EVD. This paper describes PostEboGui Programme, constraints and changes to the initial proposal, participants, first results, and new issues, 1 year after its start, in a descriptive and critical view. We started also to work on ethical aspects in the context of epidemics and of mass interventions with a risk of overinvestigation of patients.

Doctors Without Borders (Médecins Sans Frontières) has developed an advocacy agenda in Cameroon to better meet its patients' needs and to simplify control of Buruli ulcers. This agenda is based on 4 priorities: diagnostic (development of a clinical score), chemotherapeutic (to envision drug administration at home, without daily hospital visits), dressings, and HIV coinfection. These priority objectives should make it possible to reduce the duration of hospitalization and limit the need for surgery.

The authors describe the results of a program for the management of Buruli ulcers in Akonolinga (Cameroon). Its principal objective is to improve the diagnosis of dermatologic lesions and thereby to improve the indications for specific antibiotic therapy. This study, conducted in February, 2013, included 271 patients. Differential diagnosis of suspicious lesions was best with diagnostic examinations completed by histologic examination of a punch biopsy sample and advice from expert dermatologists.

In Senegal, the Expanded Programme of Immunization started by 1986 as a routine programme targeting 7 diseases: tuberculosis, tetanus, diphtheria, pertussis, poliomyelitis, measles and recently yellow fever Immunization against hepatitis B and Haemophilus influenzae b are proposed since 2005, but not implemented yet. In addition, there are mass immunization campaigns, such as National Immunization Day organized every year since 1999 against poliomyelitis and, in case of outbreak, against meningitis or yellow fever. In a 30,000 inhabitants rural study zone, vaccine contacts of children under 15 years of age are updated regularly several times a year since 1984. We also performed yearly cross sectional surveys from 1999 to estimate vaccine coverage in children of 24 months of age. Immunization status was assessed by vaccination cards presented by the children's parents and registers of health centres. We compared the results from both longitudinal and cross sectional surveys, which showed some differences. The last method seemed to indicate higher immunization rates. The vaccine coverage was slightly but not significantly higher in the study zone compared to the general vaccine coverage in Senegal, excepted for measles immunization for which the coverage was significantly lower in Niakhar. However results showed that interventions of all types lead to a high vaccine coverage (up to 80%) but are not sustainable. In the intervals, vaccine coverage decreased dramatically (below 40%), due mainly to irregular supply of antigens and poor accessibility of health facilities. Other factors are mentioned.

Background: Cluster sampling is commonly used since it does not require a sampling frame which lists all the individual enumeration units. However, this sampling design is often less precise than simple random sampling due to frequent homogeneity of individuals within clusters. This note illustrates that the precision of parameters such as mean, prevalence and odds ratio can be biased when the data analysis ignores the sampling design, yielding to possibly erroneous conclusions., Methods: Data from a cluster sampling among clandestine sex workers in Senegal were used. Two analyses were performed and their results were compared. The first analysis took into account the sampling design (design-based analysis) while the second did not (naïve analysis)., Results: The range of confidence intervals in design-based analysis differed from -43% to +84% with regard to those of naive analysis, and different conclusions could be drawn. For instance, the human immunodeficiency virus (HIV) infection in clandestine sex workers was associated with condoms use and perceived risk of HIV infection in design-based analysis but not in naive analysis., Conclusion: The data analysis must take into account the sampling design, and this is facilitated by the availability of statistical software with survey analysis capabilities.

Objectives: The aim of this paper is to study the use of verbal autopsy in order to assess maternal mortality indicators in rural settings and to determine the limits and difficulties related to that practice., Material and Methods: This study was carried out in 3 rural sites (Niakhar in the region of Fatick, Bandafassi in Tambacounda region and Mlomp in the region of Ziguinchor). These sites had been under demographic and epidemiological surveillance for several years. Data were collected through two sources: a questionnaire filled out by data collectors during the demographic surveillance and a complementary survey done by an epidemiologist among families completed by information from the registers of health structures. For all female deaths (15-49 years), the detailed sequence of the events leading to the death were stated in a clinical file of verbal autopsy. All the files had been submitted to two independent obstetricians for analysis. The character of maternal death and the cause of the death (direct, indirect ou undetermined) were processed. The discordant cases were submitted to another expert epidemiologist for analysis. The 10th international classification of diseases of WHO was used as a reference to identify maternal deaths and their causes., Results: This demographic surveillance has led to a complete registration of female deaths and the analysis of female deaths has helped to measure maternal indicators during the observed time period. Among the 471 female deaths, 97 maternal deaths were identified in Niakhar, 36 in Bandafassi and 10 in Mlomp. The proportion of maternal deaths was 30.6% in Niakhar, 32.7% in Bandafassi and 22.7% in Mlomp. The ratio of maternal mortality was 575 per 100,000 live births (LB) in Niakhar, 930/100,000 live births in Bandafassi and 436/100,000 LB in Mliomp. The risk of maternal death was 1 women in 21 in Niakhar, 1 in 16 in Bandafassi and 1 in 41 in Mlomp. Maternal mortality rate was 13.3/10,000 reproductive age women in Niakhar, 17/10,000 in Bandafassi and 6.9/10,000 in Mlomp. Sociocultural limits related to interdiction in the society, and language barriers are seen as limits for applying verbal autopsy practices. Also, a lack of precision in data collection because of lack of information delivered by the interviewee or because of lack of experience of the interviewer could be limitations. This study carried out in a rural setting could not show national maternal mortality level. It takes time to complete verbal autopsy leading to excessive cost., Conclusion: Verbal autopsy remains an interesting method for measuring maternal mortality. It has advantages in rural areas where many deliveries still occur at home. Further accuracy in data collection is needed for a precise analysis of each case.

The aim of this study lies in the identification of human activities responsible for the transmission of the Guinea worm in an endemic village in Diema Region in Mali. Human water contacts observations started after a census followed by the implementation of a bi-monthly notification system, carried out from May to November 1993. Water contacts were noticed and observed from the mid-July to the end of November of the same year. The first case of dracunculiasis observed was randomly drawn out of a list of the families with obvious cases. The patent case activities involving either surface water, traditional wells or bore-hole water were recorded for 10 consecutive days. During this observation period, contacts made by other patients with the same water sources were also recorded. After 14 days, the case list was updated and a new case selected out of families previously selected. This cycle was repeated until the end of the study period. A "contact at risk for transmission" was defined by a close correspondence between the location of the worm's emergence and the surface of the skin exposed to water, within two weeks following emergence. Contacts were described according to water sources, activities in relation to water, date, gender and age. Observations were made on 103 patients who had 2506 activities in relation with a water body: 1132 of these activities implied a skin contact with the water. Only 133 (9%) of these water contacts were at risk for transmission, 75% took place during the months of August and September, 80% were related to surface waters and 20% to traditional wells. Woman household activities and boys games were the major activities at risk, in contrast to economic activities (watering cattle). The low proportion of "at risk activities" evaluated in this study suggests that a small number of water contacts is sufficient to maintain the transmission. The case implications of the current eradication strategy might not be sufficient alone to break the transmission and should therefore be associated with a reinforcement of the use of filters for drinking water together with an health education.

The investigation of this outbreak took place in Niakhar (IRD project study area), a rural area located 150 km East of Dakar. Covering 30 villages, with a population of about 30,000 inhabitants, the area has been under demographic and epidemiological surveillance. In 1999, the surveillance allowed 973 cases of shigellosis to be recorded out of 1,751 cases of dysenteric diarrhoeas. The outbreak reached a peak during the raining season (73% of the cases in September and October). All the villages and all age groups were concerned. The attack rate in the population was 3%. During the same period, 22 deaths were attributed to shigellosis, leading to a lethality of 2.3%. Children under five were the most affected. The bacteriological examination isolated S. flexneri in 72% of 12 stools samples and S. dysenteriae A1 (SD1) in 14%. All serotypes were resistant to ampicillin and susceptible to quinolones. Susceptibility to cotrimoxazole was unconstant. Apart from the usual factors involved in the spread of diarrhoeas, the main reason evoked to explain the duration of the epidemic has been the lack of adequate emergency antibiotherapy treatment. Quinolones, recommended by the health authorities, could not be provided by health services. The identification of the SD1 serotype confirmed its involvement in the outbreak of shigellosis. The exact role of S. flexneri in shigellosis epidemics should be further studied.

There are a number of reasons why climate, in certain physical and social environments, could have an impact on the epidemiology of malaria. Events, such as floods or drought, are related to the number of malaria cases and deaths, both seasonally and interannually. At a smaller scale, this study analyses the relation between climate variability and the variability in the number of deaths attributable to malaria in Niakhar, Senegal. The Niakhar area has a population of 30,000 and has been under demographic surveillance system since 1984. The rainfall in this region is highly seasonal, with a rainfall maximum in August and almost no rain between October/November and May/June. In addition to this seasonal cycle, rainfall also varies greatly from year to year (interannual variation). Over the 13 years, there were 661 deaths attributed to malaria with a marked interannual variability (range from 23 to 100, with a median of 43). There was also a strong seasonality in mortality, with nearly all deaths (89.1%) occurring between August and December. The number of deaths peaks in October, two months after the rainfall peak. Standardised monthly values were calculated for each climatic series (rainfall, relative humidity, temperature) as well as standardised five-month and monthly values of the number of deaths attributed to malaria between August and December. Correlation coefficients were calculated between these standardised values. The correlation between the variability in August rainfall and the variability in the number of deaths attributed to malaria between August and December was positive and statistically significant (r = +0.61, p = 0.02). In addition, highly significant cross-correlations were found between monthly rainfall series and monthly mortality series at one- and two-month lag (r = + 0.43, p = 0.0004 for one-month lag; r = + 0.26, p = 0.03 for two-month lag). This correlation is somewhat lower than the correlation of August rainfall alone with August to December mortality, but the result adds confidence to the signal given the increased degrees of freedom in the analysis. Similar, but slightly weaker, results were found when precipitation data were replaced with surface humidity data. Results with temperature were less clear; while temperature could in some circumstances have a direct impact on malaria, in this case here it is possible that the weak negative correlation between malaria deaths and temperature arises mainly because precipitation is physically connected to both the indices, correlating positively with malaria and negatively with temperature. The availability of a continuous demographic and medical survey since 1984 in a region of highly variable rainfall has created a rare opportunity to analyse with some confidence a climate versus malaria relationship. The findings are consistent with our understanding of the proposed link between rainfall and conditions for the reproduction of the malaria vector, leading to a lag time (here of one to two months) between anomalies of rainfall and deaths attributable to malaria. These results may have practical implications in Sub-Saharan regions marked by a great seasonal and interannual variability in rainfall by providing a simple tool to forecast the impact of climate variability on malaria mortality.

A comparison between a digestion-sedimentation technique (DST) and the Kato-Katz thick smear technique (KKT) in the detection and quantification of Schistosoma eggs in stool was carried out in 551 subjects. Specimen were collected one or two years after treatment with praziquantel from subjects living in a schistosomiasis endemic area of Mali. One hundred infections missed by the KKT were detected by the DST. Conversely, 35 infections missed by the DST were detected by the KKT (88% were light infections). More subjects were classified as lightly infected by the DST (p < 10(-3)) and more subjects were classified as moderately infected (101-400 epg) by the KKT (p = 0.02). The KKT produced higher counts than the DST among the youngest age group which was also the most infected. The principal advantage of the DST over the KKT was its better sensitivity to detect light infections resulting from a larger amount of stool processed.

Objective: Few prospective studies have been undertaken of maternal mortality in sub-Saharan Africa. National statistics are inadequate, and data from hospitals are often the only source of information available. Reported maternal mortality ratios may therefore show large variations within the same country, as in Mali. This study was designed to produce an estimate of the maternal mortality ratio for the population of Bamako., Design: Prospective cohort study., Setting: Bankoni (population 59,000), a district of Bamako (population 700,000)., Population: 5782 pregnant women identified during quarterly household visits., Methods: After enrolment, two follow up visits, at six weeks and one year after delivery, were performed to collect information on the pregnancy, its outcome, the method of delivery, the puerperium and the first year after birth. Detailed inquiries on deaths were undertaken in the community, the maternity units and the reference hospital., Main Outcome Measures: Maternal mortality ratio, late maternal mortality, likely cause of death., Results: Complete data at follow up were available on 4717 women (82%) (4653 single and 64 twin pregnancies). Most of the women had antenatal care were and delivered in a district maternity hospital. There were 4580 live births (96%). Fifteen maternal deaths were recorded, yielding an overall maternal mortality ratio of 327 per 100,000 live births. Hypertensive disorders and haemorrhage were the main causes of death. Five more deaths occurred within 42 days or one year after delivery., Conclusions: This study gave an estimate of the maternal mortality ratio for the population of Bamako, and stressed the need of better emergency obstetric care and the importance of late maternal mortality.

There have been many cholera outbreaks in Senegal since 1971. The last outbreak began in the Dakar region in August 1995. It spread to the Diourbel, Fatick, Saint-Louis and Thies regions. In January 1996, the outbreak hit the Niakhar study area in the Fatick region. A team from ORSTOM (the French Institute of Scientific Research for Development in Cooperation) has been recording demographic events in this area for almost 15 years. The geographic approach is based on the automated mapping of cholera in hamlets and villages. Such studies investigate the factors determining the spread of diseases, within the context of land use. Three sets of data were used: demographic data that had been routinely collected and were available from a database, digitized maps and epidemiological data from a surveillance system set up to monitor the outbreak. A series of incidence maps, over time and on various scales, were generated using specialized software. The maps were analyzed and the outbreak was found to be heterogeneous over time. There were two waves of the outbreak and differences according to age and gender. The degree of heterogeneity depended on the place of residence. Heterogeneity was probably determined by village size, roads and the concentration of inhabitants within hamlets, which is roughly equivalent to the number of people per bore hole. These preliminary results suggest that further research is necessary, looking at different geographical scales (e.g. households, districts and regions). Qualitative studies of water use and the organization of the water supply are also required.

The effect of age, previous intensity of infection, and exposure on reinfection with Schistosoma haematobium after treatment was studied in a cohort of 468 subjects six years of age and over living in an irrigation scheme area in Mali. Prevalence and intensity of S. haematobium infection were measured each year between 1989 and 1991, but the reinfection study period was restricted to the last year of the follow-up. Observations were made at the principal water contact sites where the number of Bulinus truncatus shedding furcocercous cercariae was recorded. A cumulative index of exposure taking into account time, duration and type of contact, and malacologic data was calculated for each subject. Univariate analysis showed that the reinfection risk decreased with age and increased with exposure and pretreatment intensity. These results were confirmed by fitting a logistic model that showed that this risk was seven times lower among those 15 years of age and older than among the 6-14-year-old children, while linear trends with exposure to infection and pretreatment intensity were significant. This study supports the concept of an age-acquired resistance to reinfection and is in favor of a predisposition to infection that raises the question of a genetic factor controlling susceptibility/resistance to S. haematobium infection.

For the period September to December 1985, 1226 water contacts were recorded during 8 days of direct observation. Various activities were analysed in order to determine their responsibility in transmission. An index of exposure, allowing for duration of contact, body surface exposed and infectiousness of the water was calculated for each contact. Domestic contacts, primarily female, represented 62% of the observations but only 15% of total exposure. Conversely, contacts for recreational purposes mainly involved young boys and accounted for 14% of the observations and 70% of total exposure. Between 6 and 20 years of age the mean index of exposure by contact was higher in males than in females. Changing water contact behavior seems to be an unrealistic means of preventing transmission in the community studied. The most appropriate strategy of control would appear to be selective treatment of heavily infected individuals.