Socio-economic risk factors for malaria in a peri-urban area of The Gambia

Household and socioeconomic factors associated with childhood febrile illnesses and treatment seeking behaviour in an area of epidemic malaria in rural Ethiopia

To assess household and socioeconomic factors associated with childhood febrile illnesses and treatment seeking behaviour, a study was conducted in Adami Tulu district in Ethiopia during the peak malaria transmission season in 2003. All mothers/caretakers of children <5 years of age were interviewed regarding their household characteristics, history of febrile illness (malaria) among children and actions taken 2 weeks prior to the survey. Of 3873 children, 21% had experienced fever in the past 2 weeks. Household ownership of a mosquito net (odds ratio (OR)=0.4, 95% CI 0.3-0.7) and prior spraying of the house with aerosols (OR=0.7, 95% CI 0.5-0.9) or DDT (OR=0.8, 95% CI 0.6-0.9) were associated with lower risk of febrile illnesses, whilst sharing the house with livestock increased the risk (OR=1.3, 95% CI 1.1-1.6). Treatment was sought for 87% of febrile children, with public facilities, private clinics and community health workers accessed fairly equally (26-27%). Home management was uncommon (6.4%). More febrile children from households in the middle (37.1%) and highest (44.6%) wealth categories sought treatment within 24h compared with the lowest category (18.3%). Widescale use of vector control measures such as mosquito nets and insecticide spraying of houses can effectively reduce the incidence of febrile illnesses among children.

Seroprevalence of malaria in inhabitants of the urban zone of Antananarivo, Madagascar

Background

Antananarivo, the capital of Madagascar, is located at an altitude of over 1,200 m. The environment at this altitude is not particularly favourable to malaria transmission, but malaria nonetheless remains a major public health problem. The aim of this study was to evaluate exposure to malaria in the urban population of Antananarivo, by measuring the specific seroprevalence of Plasmodium falciparum.

Methods

Serological studies specific for P. falciparum were carried out with an indirect fluorescent antibody test (IFAT). In a representative population of Antananarivo, 1,059 healthy volunteers were interviewed and serum samples were taken.

Results

The seroprevalence of IgG+IgA+IgM was 56.1% and that of IgM was 5.9%. The major risk factor associated with a positive IgG+IgA+IgM IFAT was travel outside Antananarivo, whether in the central highlands or on the coast. The abundance of rice fields in certain urban districts was not associated with a higher seroprevalence.

Conclusion

Malaria transmission levels are low in Antananarivo, but seroprevalence is high. Humans come into contact with the parasite primarily when travelling outside the city. Further studies are required to identify indigenous risk factors and intra-city variations more clearly.

Pallor as a sign of anaemia in small Tanzanian children at different health care levels

BACKGROUND

Anaemia is a major complication of Plasmodium falciparum malaria among small children in sub-Saharan Africa. We studied the performance of the Integrated Management of Childhood Illness (IMCI) recommended assessment of no/some/severe pallor as predictor of anaemia in health surveys at community level and in clinical practice in an out patient department (OPD) and in a hospital ward in rural Tanzania.

METHODS

The study was undertaken among 6-36 months old children. Pallor was evaluated as a combined assessment of conjunctiva, tongue and palms and categorised as no, some or severe pallor. Packed cell volume (PCV) was measured and related to pallor.

FINDINGS

A total of 740 examinations were performed at village, OPD and in the hospital ward. The prevalences of severe pallor were 0%, 1.5% and 7% respectively. The prevalences of any pallor were 14%, 41% and 86%. The prevalences of severe anaemia (PCV<21%) were 1%, 5% and 81% and of any anaemia (PCV<33%) 68%, 73% and 98%. Severe pallor could not detect severe anaemia. The sensitivities were only 0%, 0% and 8%. The sensitivities of any pallor to detect severe anaemia were however 86% and 98% for children at the health care facility level, but still of relatively poor predictive values since the specificities were only 61% and 68%.

INTERPRETATION

Division of pallor into some or severe degrees was of no use at any health care level. The identification of any pallor was of no use at village level, but it may possibly be of some value as a screening test for severe anaemia at health care facilities, if additional assessment is included in view of the low specificity and positive predictive value of the finding.

Urban malaria and anaemia in children: a cross-sectional survey in two cities of Ghana

OBJECTIVE

To describe the epidemiology of urban malaria, an emerging problem in sub-Saharan Africa.

METHOD

Cross-sectional surveys of communities in Accra and Kumasi, Ghana, determining risk factors for malaria infection and anaemia in children aged 6-60 months.

RESULTS

Malaria prevalence rates ranged from 2% to 33% between urban communities. 47.1% of children were anaemic (Hb<11.0 g/dl). Factors associated with malaria prevalence were low socio-economic status, age and anaemia. The attributable risks of anaemia and severe anaemia (Hb<8.0 g/dl) caused by malaria were 5% and 23% respectively.

CONCLUSIONS

Malaria in urban areas displayed a heterogeneity and complexity that differed from the rural environment, which has important implications for malaria control. Marked intra-city variation indicates the importance of targeting specific areas or districts. The most vulnerable group, the urban poor, should be prioritized when designing control measures. This would require careful assessment of the malaria risk pattern in any city to guide an integrated control program.

Self-reported malaria and mosquito avoidance in relation to household risk factors in a Kenyan coastal city

A geographically stratified cross-sectional survey was conducted in 2002 to investigate household-level factors associated with use of mosquito control measures and self-reported malaria in Malindi, Kenya. A total of 629 households were surveyed. Logistic regressions were used to analyse the data. Half of all households (51%) reported all occupants using an insecticide-treated bed net and at least one additional mosquito control measure such as insecticides or removal of standing water. Forty-nine per cent reported a history of malaria in the household. Of the thirteen household factors analysed, low (OR=0.23, CI 0.11, 0.48) and medium (OR=0.50, CI 0.29, 0.86) education, mud--wood--coral (OR=0.0.39, CI 0.24, 0.66) and mud block--plaster (OR=0.47, CI 0.25, 0.87) wall types, farming (OR=1.38, CI 1.01, 1.90) and travel to rural areas (OR=0.48, CI 0.26, 0.91) were significantly associated with the use of mosquito control, while controlling for other covariates in the model. History of reported malaria was not associated with the use of mosquito control (OR=1.22, CI 0.79, 1.88). Of the thirteen covariates analysed in the second model, only two household factors were associated with history of malaria: being located in the well-drained stratum (OR=0.49, CI 0.26, 0.96) and being bitten while in the house (OR=1.22, CI 0.19, 0.49). These results suggest that high socioeconomic status is associated with increased household-level mosquito control use, although household-level control may not be enough, as many people are exposed to biting mosquitoes while away from the house and in areas that are more likely to harbour mosquitoes.

Malaria in southern Mozambique: incidence of clinical malaria in children living in a rural community in Manhiça district

We estimated the incidence of clinical malaria episodes by weekly home-based active case detection between December 1996 and July 1999 in 2 groups of children in Manhiça district in southern Mozambique. Cohort 1 comprised a random sample of children aged <10 years at recruitment and cohort 2 comprised newborns. A blood slide was taken if the axillary temperature was 7.5 degrees C or if the child was reported to have been febrile over the previous 24 h. A total of 1966 children were followed-up. Malaria occurred all year round. The number of clinical malaria episodes ranged from 0 to 6 per child. No clinical malaria episodes were detected in 71% of children or in children aged <2 months. Those aged 6 months to <4 years showed the highest incidence ranging from 0.65 to 0.74 episodes per 100 person-weeks at risk, indicating that infants and young children were at highest risk. Malaria transmission is perennial in this district of Mozambique with some seasonality. Significant differences were observed in the spatial incidence of malaria episodes in regions just a few miles apart with a higher incidence in children living near the river or in swampy areas. These findings strengthen the need for improved control measures targeted at infancy and early childhood.

Is malaria a disease of poverty? A review of the literature

OBJECTIVE

To review the evidence on the link between malaria and poverty.

METHODS

Review of the published and grey literature to identify (i) the data available on the socio-economic distribution of malaria incidence and vulnerability, and (ii) the uptake of malaria control interventions.

RESULTS

We found mixed evidence on malaria incidence, with a number of studies identifying no relationship between socio-economic status and incidence, although a larger number of studies do find a link. There is strong evidence that uptake of preventive and treatment interventions is closely related to proxies for socio-economic status. More generally, the quality of the literature examining this issue is highly variable, with many different measures of socio-economic status and often inadequate descriptions of methods of data collection and analysis in relation to socio-economic status.

CONCLUSIONS

Important socio-economic differentials exist in access to malaria interventions, increasing the vulnerability of the poorest. More information is needed about how other methods of delivering malaria treatment and prevention can redress these inequalities.

Spatial clustering of malaria and associated risk factors during an epidemic in a highland area of western Kenya

The epidemiology of malaria over small areas remains poorly understood, and this is particularly true for malaria during epidemics in highland areas of Africa, where transmission intensity is low and characterized by acute within and between year variations. We report an analysis of the spatial distribution of clinical malaria during an epidemic and investigate putative risk factors. Active case surveillance was undertaken in three schools in Nandi District, Western Kenya for 10 weeks during a malaria outbreak in May-July 2002. Household surveys of cases and age-matched controls were conducted to collect information on household construction, exposure factors and socio-economic status. Household geographical location and altitude were determined using a hand-held geographical positioning system and landcover types were determined using high spatial resolution satellite sensor data. Among 129 cases identified during the surveillance, which were matched to 155 controls, we identified significant spatial clusters of malaria cases as determined using the spatial scan statistic. Conditional multiple logistic regression analysis showed that the risk of malaria was higher in children who were underweight, who lived at lower altitudes, and who lived in households where drugs were not kept at home.

Association between climate variability and malaria epidemics in the East African highlands

The causes of the recent reemergence of Plasmodium falciparum epidemic malaria in the East African highlands are controversial. Regional climate changes have been invoked as a major factor; however, assessing the impact of climate in malaria resurgence is difficult due to high spatial and temporal climate variability and the lack of long-term data series on malaria cases from different sites. Climate variability, defined as short-term fluctuations around the mean climate state, may be epidemiologically more relevant than mean temperature change, but its effects on malaria epidemics have not been rigorously examined. Here we used nonlinear mixed-regression model to investigate the association between autoregression (number of malaria outpatients during the previous time period), seasonality and climate variability, and the number of monthly malaria outpatients of the past 10-20 years in seven highland sites in East Africa. The model explained 65-81% of the variance in the number of monthly malaria outpatients. Nonlinear and synergistic effects of temperature and rainfall on the number of malaria outpatients were found in all seven sites. The net variance in the number of monthly malaria outpatients caused by autoregression and seasonality varied among sites and ranged from 18 to 63% (mean=38.6%), whereas 12-63% (mean=36.1%) of variance is attributed to climate variability. Our results suggest that there was a high spatial variation in the sensitivity of malaria outpatient number to climate fluctuations in the highlands, and that climate variability played an important role in initiating malaria epidemics in the East African highlands.

Which children come to the health centre for treatment of malaria?

Malaria remains one of the major public health problems for children in Guinea-Bissau and the major reason for using the health services. Little is known about factors with impact on whether the mothers seek malaria treatment for their children at a health centre. Mothers of children coming to the Bandim Health Centre in Bissau and age-matched controls selected from the registration system of the Bandim Health Project were interviewed about treatment habits, socio-economic standards and other factors associated with the mother seeking treatment for her child at a health centre. In a multivariate analysis, the controls were more often found to have chloroquine at home and had more often taken home treatment for suspected malaria. On average 2.97 persons among cases shared bed as opposed to only 2.02 among controls, bed-crowding thus, being a factor determining health seeking behaviour (P=0.0001). Low socio-economic status, as measured by the non-availability of electricity, was also a significant predicting factor (P=0.02). The possibilities of promoting home treatment should be further evaluated, not only to avoid unnecessary visits to the professional health system, but also to decrease the morbidity from acute malaria.

Reducing malaria by mosquito-proofing houses

Sometimes, valuable lessons from history are forgotten, remain unknown, or worse, are ignored. This article reminds us of the pioneering work of Angelo Celli at the end of the 19th century, who demonstrated that people could be protected from malaria by screening their homes against mosquitoes. Since then, public health scientists have continued to show that simple changes in house design have the potential for protecting people against this life-threatening disease. Yet today, this type of intervention remains virtually ignored. The literature reviewed here demonstrates the enormous potential of these methods to reduce malaria, in the hope that it will stimulate scientific debate and further research.

Environmental risk factors for clinical malaria: a case-control study in the Grau region of Peru

The role of environmental risk factors in clinical malaria has been studied mainly in Africa and Asia, few investigations have been carried out in Latin America. Field observations in northern coastal Peru, where the prevalence of malaria is high during the agricultural season, suggested that the risk of disease varied according to the characteristics of the house and the house environment. Environmental determinants of the risk of clinical malaria were therefore investigated through a case-control study: 323 clinical cases of malaria, recruited through community-based active case-finding, and 969 age-, sex- and village-matched controls were recruited into the study over a period of 12 months ending June 1997. Residual spraying of houses in the previous 6 months, living more than 100 m from a canal, a level of education equal to primary school or above and working in agriculture conferred significant protection from the risk of developing clinical malaria. The presence of spaces between the wall and roof in the subject's bedroom (eaves) and a house aged > 4 years statistically significantly increased the risk of disease. Based on these results we discuss possible control measures for malaria in this area of the country.

Application of log-linear models to malaria patients in Thailand

Malaria is a common infectious disease in many tropical countries, including Thailand. The country is located geographically in a tropical zone and the transmission of malaria is particularly common in some regions, for instance in Tak province. The objective of this study is to identify risk factors causing malaria in Tak province in the rainy season by using log-linear models. Tests of independence are used (chi-square and Cramer's V-value tests) to find out the relationships between any two variables. In addition two- and three-dimensional log-linear models are used to obtain estimated parameters and expected frequencies for these models. Amongst the models fitted, the best are chosen based on the analysis of deviance. The results of this study show that most observed variables are significantly related with p-values<0.05. Causes of migration and reasons for staying overnight are highly related to personal variables. Thus, it can be concluded that two of the risk factors for malaria are causes of migration and reasons for staying overnight. Knowledge of prevention is also related to personal variables. Therefore, knowledge of prevention was concluded to be a risk factor affecting prevalence of malaria. For each set of three variables, the best model shows interaction terms of variables that have a relationship but there are no interactions of three effects in these best models.

Risk factors associated with malaria infection in an urban setting

Incidence of malaria in urban settings is a growing concern in many regions of the world and individual risk factors need to be identified to appropriately adjust control strategies. We carried out a cross-sectional study in 1993/94 in an urban area of the largest port of the Pacific Coast of Colombia, where transmission has had an upward trend over the past 5 years. Prevalence of malaria infection was estimated in areas of the city with the highest incidence of disease, and the association between some characteristics of the population and the risk of malaria infection was assessed. Prevalence of malaria infection was 4.4% among the 1380 studied people and we found that it decreased with older age, and with knowledge of disease and preventive measures directed to elimination of breeding sites. In addition, the infection was positively associated with exposure to the forest (P < 0.05), although most of the cases (57/61, 93%) were likely to have been acquired in the urban area. We also found that individuals receiving antimalarial treatment in the previous month had around twice the risk of being infected as compared with those without treatment. In addition, our results suggest that use of bednets could not be a very effective protective measure in settings such as that of our study, and that environmental interventions may be needed to decrease the risk of infection.

Household risk factors for malaria among children in the Ethiopian highlands

Malaria transmission varies from village to village and even from family to family in the same village. The current study was conducted in northern Ethiopia to identify risk factors responsible for such variations in a hypoendemic highland malaria setting: 2114 children aged < 10 years living in 6 villages situated close to small dams at altitudes from 1775 to 2175 m were monitored. Monthly malaria incidence was determined 4 times over a 1-year period during 1997. Incidence results were then analysed by 14 individual and household factors using Poisson multivariate regression. Among 14 factors analysed, use of irrigated land (rate ratio[RR] = 2.68, 95% CI 1.64-4.38), earth roof (RR = 2.15, 95% CI 1.31-3.52), animals sleeping in the house (RR = 1.92, 95% CI 1.29-2.85), windows (RR = 1.84, 95% CI 1.30-2.63), open eaves (RR = 1.85, 95% CI 1.19-2.88), no separate kitchen (RR = 1.57, 95% CI 1.10-2.23), and 1 sleeping room (RR = 1.52, 95% CI 1.05-2.20), were significantly associated with malaria. The proportion of infection among children exposed to one or no risk factor was 2.1%, increasing with the number of risk factors and reaching 29.4% with 5 or more. Further studies are needed to confirm the importance of particular risk factors, possibly leading to simple health education and control measures that could become part of routine control programmes, implemented with inter-sectoral collaboration.

Knowledge, beliefs and practices relevant for malaria control in an endemic urban area of the Colombian Pacific

Research projects for malaria control must involve communities to elicit strategies to be successful and programs to be sustainable. Therefore, knowledge, beliefs and practices of the population concerned must be taken into account in the design of interventions against malaria transmission. We conducted a KAP study in Buenaventura, a port on the Pacific Coast of Colombia where transmission was on the increase at the beginning of this decade. The purpose of the study was to help in the design and implementation of a primary health care approach for malaria control. Both qualitative and quantitative research methods were used. The focus group technique was applied in five urban and peri-urban communities and a cross sectional survey was conducted on a random sample of 1380 subjects with a structured interview on knowledge, practices and also on demographic and epidemiological aspects. The information obtained by the two methods was comparable on knowledge of symptoms, causes and ways of malaria transmission, and prevention practices like the use of bednets or provision of health services. We discuss the relevance of obtaining this information and analyze the elements that must be taken into account for communities to become more involved in malaria control strategies.

No influence of socioeconomic factors on severe malarial anaemia, hyperparasitaemia or reinfection

Malaria is responsible for nearly 500 million clinical cases per year, only a small proportion of whom will become severely ill. Socioeconomic risk factors may play a role in the development of severe malaria in African children and in their susceptibility to reinfection. In Gabon, 100 children suffering from severe malaria, defined as hyperparasitaemia and/or severe anaemia, were matched for sex, age and provenance to 100 children with mild malaria. Socioeconomic factors were assessed using a standard questionnaire and compared between the 2 groups. The children were followed-up and the time to first reinfection was recorded. No significant influence of socioeconomic factors could be detected on the severity of disease or the time to first reinfection. Socioeconomic factors are not major determinants of severe malarial anaemia and hyperparasitaemia in children in Gabon.

Environmental and entomological risk factors for the development of clinical malaria among children on the Kenyan coast

Several malariometric studies have examined the impact on human-vector contact of house construction, demographics, bed net and insect repellent use. However, few studies have documented the significance of these proximate determinants on the risks of clinical disease. We undertook a matched case-control study of the risks of both mild clinical malaria and severe life-threatening malaria according to a range of putative factors which would influence the frequency of child-vector encounters in Kilifi district on the Kenyan coast. Among 394 severe disease cases, 380 age-matched mild disease cases, and their respective location and age-matched community controls, we were unable to demonstrate any statistically significant effect upon disease outcome of house construction, presence of domestic animals, or bed net use. Higher population density within a 250 m radius of the homes conferred significant protection from the risks of developing severe malaria compared to community controls. The risks of developing severe malaria compared to the community controls and the transition from mild to severe disease were statistically significantly lower in those who reported use of mosquito coils, local repellents or aerosol insecticides. We concluded that it is likely that the impact of household features on disease outcome is dependent upon both the density of infecting mosquitoes and acquired immunity within a given locality.

Risk factors for malaria: a microepidemiological study in a village in Sri Lanka

Environmental and socioeconomic risk factors for malaria were studied in a village in Sri Lanka. Over a period of one year, all 49 households in the village were visited every alternate day to obtain information on malaria episodes. Information on risk factors was obtained through questionnaires and direct observations. Age below 17 years (relative risk [RR] = 1.66, 95% confidence interval [95% CI] 1.18-2.35), use of bed nets (RR = 0.16, 95% CI 0.05-0.45) and traditional fumigants (RR = 0.58, 95% CI 0.37-0.93) were independent predictors of malaria. People using anti-mosquito pyrethrum coils had a higher risk for malaria than people living in houses where they were not used (RR = 1.46, 95% CI 1.03-2.07). The build-up of Anopheles culicifacies populations before the start of the transmission season had taken place in a stream near the village. Living close to the stream was a risk factor for malaria early in the transmission season, although this did not reach statistical significance (comparing < 250 m with > 500 m, RR = 2.13, 95% CI 0.96-4.71).

The Gambian National Impregnated Bed Net Programme: evaluation of effectiveness by means of case-control studies

Two case-control studies, one on mortality and the other on malaria morbidity, were carried out in order to evaluate the impact of the Gambian National Insecticide Bed Net Programme during the second year of intervention and to explore the feasibility of such a study for the evaluation of programme effectiveness. For the mortality study, children 1-9 years old who died during the 1993 rainy season were matched by age and sex with 2 healthy controls from the same village. For the morbidity study, children 1-9 years old attending Fatoto or Jahalia Health Centres in The Gambia and who had fever and parasitaemia > or = 5000/microL were matched by age with a child attending the health centres without fever or parasitaemia. An additional healthy control was recruited from the case's village. No impact of insecticide-treated bed nets on mortality was detected and this was in keeping with the results obtained by prospective surveillance. A protective effect of insecticide-treated nets on malaria morbidity was detected when cases were compared with controls recruited at the health centres. However, this disappeared when cases were compared with controls recruited from the cases' villages. The mortality case-control study suggested that reducing the time between onset of disease and treatment may have an important impact on childhood mortality. In order to calculate programme cost-effectiveness, important for informed resource allocations to be made by health managers, it is essential to obtain evidence of effectiveness. This can be done by means of case-control studies, which are easier to carry out and require fewer resources than prospective surveillance. Nevertheless, it is necessary to be conscious of their pitfalls, particularly of the bias involved in the choice of cases and controls. The measurement of insecticide on the nets of the cases or controls is essential for such studies.

Socio-economic determinants are not major risk factors for severe malaria in Gambian children

Only a small proportion of subjects infected with Plasmodium falciparum develop severe disease. Why this should be is not fully understood. To investigate the possible importance of socio-economic variables on the severity of malaria in Gambian children we undertook a case-control study of 384 children with severe or mild malaria. Few differences were found between the 2 groups. Children with severe malaria had a longer duration of symptoms when recruited than mild cases but this difference was largely accounted for by the fact the most children with severe disease were recruited at a referral hospital, whilst mild cases were recruited at a primary health care facility nearer their home. There was no difference between groups in the time before mothers sought some form of health care. Mothers of children with severe disease were less ready to take their child to hospital than mothers of mild cases, suggesting that education on the importance of taking a child with features of malaria to a health centre as soon as possible might have some effect on the development of severe disease. However, overall, the results of this study suggested that socio-economic and behavioural factors are not the major determinants for severe malaria in African children.