Prevalence of malaria parasitemia among clients seeking treatment for fever or malaria at drug stores in rural Tanzania 2004

OBJECTIVE: To determine the prevalence of malaria parasitemia and other common illnesses among drug store clients in one rural community, with a view to the potential role of specialist drug stores in expanding coverage of effective malaria treatment to households in highly endemic areas. METHOD: Follow-back study of 2466 client visits selected from all 10 drug stores operating in the town of Ikwiriri between May 30 and August 31 2004. Of these, 521 (21.2%) were made by or on behalf of persons ill with fever or malaria. Two hundred and ninety three were eligible as residents of the surrounding nine villages and all agreed to participate in the study. Each patient was evaluated by a clinical officer and provided a blood sample for malaria on the day of the shop visit, either at the shop or at home. RESULTS: Only 50 (17.1%) visits by or on behalf of febrile patients resulted in the purchase of an antimalarial drug, while an antipyretic medication was obtained at 226 visits (77.1%). Clinicians diagnosed malaria in 63.8% of patients. Malaria parasites were identified in blood film samples from 24.2% (95% CI: 19.6, 29.5). This is double the parasite prevalence rate of 10.7% (95% CI: 8.6, 13.1) obtained from a household survey of 1004 healthy individuals selected from these villages at the same time. It is not significantly lower than the prevalence observed among 880 clients presenting with fever at health facilities in the district: 29.7% (95% CI: 23.0, 37.3). The prevalence of malaria parasitemia among children younger than 5 years whose families sought fever treatment from drug stores (42.1%; 95% CI: 31.4, 53.5) was equal to that of children presenting with fever at health facilities (42.5%; 95% CI: 25.0, 62.2). CONCLUSIONS: Currently, drug store clients do not obtain malaria-specific treatment in the majority of cases where it might be warranted. Parasitological findings indicate that drug store clients, especially children, are as likely to be infected with malaria as patients seeking care for similar illnesses at health facilities. Drug stores may be attractive partners for policy makers eager to engage the private retail sector in expanding coverage of malaria treatment.     

Malaria prevalence and treatment of febrile patients at health facilities and medicine retailers in Cameroon

Objective To investigate the quality of malaria case management in Cameroon 5 years after the adoption of artemisinin‐based combination therapy (ACT). Treatment patterns were examined in different types of facility, and the factors associated with being prescribed or receiving an ACT were investigated. Methods A cross‐sectional cluster survey was conducted among individuals of all ages who left public and private health facilities and medicine retailers in Cameroon and who reported seeking treatment for a fever. Prevalence of malaria was determined by rapid diagnostic tests (RDTs) in consenting patients attending the facilities and medicine retailers. Results Among the patients, 73% were prescribed or received an antimalarial, and 51% were prescribed or received an ACT. Treatment provided to patients significantly differed by type of facility: 65% of patients at public facilities, 55% of patients at private facilities and 45% of patients at medicine retailers were prescribed or received an ACT (P = 0.023). The odds of a febrile patient being prescribed or receiving an ACT were significantly higher for patients who asked for an ACT (OR = 24.1, P < 0.001), were examined by the health worker (OR = 1.88, P = 0.021), had not previously sought an antimalarial for the illness (OR = 2.29, P = 0.001) and sought treatment at a public (OR = 3.55) or private facility (OR = 1.99, P = 0.003). Malaria was confirmed in 29% of patients and 70% of patients with a negative result were prescribed or received an antimalarial. Conclusions Malaria case management could be improved. Symptomatic diagnosis is inefficient because two‐thirds of febrile patients do not have malaria. Government plans to extend malaria testing should promote rational use of ACT; though, the introduction of rapid diagnostic testing needs to be accompanied by updated clinical guidelines that provide clear guidance for the treatment of patients with negative test results.     

Health workers' use of malaria rapid diagnostic tests (RDTs) to guide clinical decision making in rural dispensaries, Tanzania

Rapid diagnostic tests (RDTs) were developed as an alternative to microscopy for malaria diagnosis. The RDTs detect malaria parasite antigen(s) in whole blood with high sensitivity and specificity. We assessed health worker malaria treatment practices after the introduction of RDTs in peripheral health facilities without microscopy. From December 2007 to October 2008, we introduced histidine-rich protein II (HRP-2)-based ParaHIT RDTs for routine use in 12 health facilities in Rufiji District, Tanzania. Health workers received training on how to perform RDTs for patients 5 years of age or older with fever or suspected malaria. Children < 5 years of age were to be treated empirically per national guidelines. Among the 30,195 patients seen at these 12 health facilities, 10,737 (35.6%) were tested with an RDT for malaria. 88.3% (9,405/10,648) of tested patients reported fever or history of fever and 2.7% (289/10,677) of all tested individuals were children < 5 years of age. The RDT results were recorded for 10,650 patients (99.2%). Among the 5,488 (51.5%) RDT-positive patients, 5,256 (98.6%) were treated with an appropriate first-line antimalarial per national guidelines (artemether-lumefantrine or quinine). Among the 5,162 RDT-negative patients, only 205 (4.0%) were treated with an antimalarial. Other reported treatments included antibiotics and antipyretics. Implementation of RDTs in rural health facilities resulted in high adherence to national treatment guidelines. Patients testing negative by RDT were rarely treated with antimalarials. Unapproved antimalarials were seldom used. Health workers continued to follow guidelines for the empiric treatment of febrile children.     

Malaria diagnosis and treatment under the strategy of the integrated management of childhood illness (IMCI): relevance of laboratory support from the rapid immunochromatographic tests of ICT Malaria P.f/P.v and OptiMal

The algorithm developed for the integrated management of childhood illness (IMCI) provides guidelines for the treatment of paediatric malaria. In areas where malaria is endemic, for example, the IMCI strategy may indicate that children who present with fever, a recent history of fever and/or pallor should receive antimalarial chemotherapy. In many holo-endemic areas, it is unclear whether laboratory tests to confirm that such signs are the result of malaria would be very relevant or useful. Children from a holo-endemic region of Tanzania were therefore checked for malarial parasites by microscopy and by using two rapid immunochromatographic tests (RIT) for the diagnosis of malaria (ICT Malaria P.f/P.v and OptiMal. At the time they were tested, each of these children had been targeted for antimalarial treatment (following the IMCI strategy) because of fever and/or pallor. Only 70% of the 395 children classified to receive antimalarial drugs by the IMCI algorithm had malarial parasitaemias (68.4% had Plasmodium falciparum trophozoites, 1.3% only P. falciparum gametocytes, 0.3% P. ovale and 0.3% P. malariae). As indicators of P. falciparum trophozoites in the peripheral blood, fever had a sensitivity of 93.0% and a specificity of 15.5% whereas pallor had a sensitivity of 72.2% and a specificity of 50.8%. The RIT both had very high corresponding sensitivities (of 100.0% for the ICT and 94.0% for OptiMal) but the specificity of the ICT (74.0%) was significantly lower than that for OptiMal (100.0%). Fever and pallor were significantly associated with the P. falciparum asexual parasitaemias that equalled or exceeded the threshold intensity (2000/microl) that has the optimum sensitivity and specificity for the definition of a malarial episode. Diagnostic likelihood ratios (DLR) showed that a positive result in the OptiMal test (DLR = infinity) was a better indication of malaria than a positive result in the ICT (DLR = 3.85). In fact, OptiMal had diagnostic reliability (0.93) which approached that of an ideal test and, since it only detects live parasites, OptiMal is superior to the ICT in monitoring therapeutic responses. Although the RIT may seem attractive for use in primary health facilities because relatively inexperienced staff can perform them, the high cost of these tests is prohibitive. In holo-endemic areas, use of RIT or microscopical examination of bloodsmears may only be relevant when malaria needs to be excluded as a cause of illness (e.g. prior to treatment with toxic or expensive drugs, or during malaria epidemics). Wherever the effective drugs for the first-line treatment of malaria are cheap (e.g. chloroquine and Fansidar), treatment based on clinical diagnosis alone should prove cost-saving in health facilities without microscopy.     

Home treatment of 'malaria' in children in rural Gambia is uncommon

Home treatment with antimalarials is a common practice in many countries, and may save lives by ensuring that more malaria cases receive prompt treatment. Through retrospective surveys we found that home treatment of young children with antimalarials was uncommon in rural Gambia. Few families kept medicines in the home in case of illness, 28% kept paracetamol and only 8% kept chloroquine. Less than 10% of cases of childhood 'malaria' had been treated with chloroquine at home, and 69% of those giving home medication did not know the correct dosage for a child. The most common course of treatment was the use of paracetamol and/or tepid sponging to reduce fever, before the child was taken to a government health facility. Treating a child with antimalarials at home was more costly than other forms of treatment. The low cost associated with the use of health services for children and the limited availability of antimalarials outside major towns contribute to the high use of government health services. This shows that that home treatment cannot be assumed to be the predominant mode of malaria treatment throughout Africa, and highlights the need for country-specific policies based on accurate local knowledge of treatment practices in both rural and urban areas.     

Predictors of treatment error for children with uncomplicated malaria seen as outpatients in Blantyre district, Malawi

BACKGROUND: Past studies have shown that health workers in developing countries often do not follow clinical guidelines, though few studies have explored with appropriate methods why errors occur. To develop interventions that improve health worker performance, factors affecting treatment practices must be better understood. METHODS: We analysed data from a health facility survey in Blantyre District, Malawi, in which health workers were observed treating ill children, and then children were independently re-examined by 'gold-standard' study clinicians. The analysis was limited to children with uncomplicated malaria (defined according to Malawi's guidelines as fever or anaemia without signs of severe illness), and a treatment error was defined as failure to treat with an effective antimalarial. RESULTS: Twenty-eight health workers and 349 ill-child consultations were evaluated; 247 (70.8%) children were treated with an effective antimalarial, and 102 (29.2%) were subject to treatment error. Logistic regression analysis revealed that in-service malaria training was not associated with treatment quality (univariate odds ratio (OR) = 1.16, 95% confidence interval (CI): 0.46-2.93); whereas acute respiratory infections training was associated with making an error (adjusted OR (aOR) = 2.42, 95% CI: 1.23-4.76). High fever and chief complaint of fever were associated with fewer errors (aOR = 0.25, 95% CI: 0.10-0.60 and aOR = 0.25, 95% CI: 0.13-0.48, respectively). Errors were more likely to occur in consultations starting before 1 p.m. (aOR = 1.88, 95% CI: 1.07-3.31). Supervision was not associated with better treatment quality. CONCLUSIONS: These results suggest that the disease-specific training and supervision, performed before the survey, did not lead to long-term improvements in health care quality. Furthermore, case management training for one specific disease may have worsened quality of care for another disease. These results support integration of guidelines for multiple conditions. Interventions should be evaluated for unintended negative effects on overall quality of care.     

Laboratory malaria diagnostic capacity in health facilities in five administrative zones of Oromia Regional State, Ethiopia

Objectives and methods Quality laboratory services are a requisite to guide rational case management of malaria. Using a pre‐tested, standardized assessment tool, we assessed laboratory diagnostic capacity in 69 primary, secondary and tertiary health facilities as well as specialized laboratories in five administrative zones in Oromia Regional State, Ethiopia, during February and March 2009. Results There was marked variability in laboratory diagnostic capacity among the facilities assessed. Of 69 facilities surveyed, 53 provided both comprehensive malaria laboratory diagnosis and outpatient treatment services, five provided malaria microscopy services (referring elsewhere for treatment), and 11 primary care health posts provided rapid diagnostic testing and outpatient malaria treatment. The facilities’ median catchment population was 39 562 and 3581 people for secondary/tertiary and primary health facilities, respectively. Depending on facility type, facilities provided services 24 h a day, had inpatient capacity, and access to water and electricity. Facilities were staffed by general practitioners, health officers, nurses or health extension workers. Of the 58 facilities providing laboratory services, 24% of the 159 laboratory staff had received malaria microscopy training in the year prior to this survey, and 72% of the facilities had at least one functional electric binocular microscope. Facilities had variable levels of equipment, materials and biosafety procedures necessary for laboratory diagnosis of malaria. The mean monthly number of malaria blood films processed at secondary/tertiary facilities was 225, with a mean monthly 56 confirmed parasitologically. In primary facilities, the mean monthly number of clinical malaria cases seen was 75, of which 57 were tested by rapid diagnostic test (RDTs). None of the surveyed laboratory facilities had formal quality assurance/quality control protocols for either microscopy or RDTs. Conclusions This is the first published report on malaria diagnostic capacity in Ethiopia. While our assessment indicated that malaria laboratory diagnosis was available in most facilities surveyed, we observed significant gaps in laboratory services which could significantly impact quality and accessibility of malaria diagnosis, including laboratory infrastructure, equipment, laboratory supplies and human resources.     

Syndromic Diagnosis of Malaria in Rural Sierra Leone and Proposed Additions to the National Integrated Management of Childhood Illness Guidelines for Fever

Many countries in Africa, including Sierra Leone, have adopted artemisinin-based combination therapy as first-line therapy for treatment of patients with malaria. Because laboratory testing is often unavailable in rural areas, the cost-benefit and viability of this approach may depend on accurately diagnosing malaria by using clinical criteria. We assessed the accuracy of syndromic diagnosis for malaria in three peripheral health units in rural Sierra Leone and determined factors that were associated with an accurate malaria diagnosis. Of 175 children diagnosed with malaria on syndromic grounds, 143 (82%) were confirmed by the Paracheck-Pf test. In a multivariate analysis, splenomegaly (P = 0.04) was the only clinical sign significantly associated with laboratory-confirmed malaria, and sleeping under a bed net was protective (P = 0.05). Our findings show that clinical malaria is diagnosed relatively accurately in rural Sierra Leone. Incorporating bed net use and splenomegaly into the national Integrated Management of Childhood Illness guidelines for evaluation of fever may further enhance diagnostic accuracy for malaria.     

Clinical case definition of malaria at a secondary level hospital in northern India

Malaria has re-emerged as a major public health problem in India. At present, under the National guidelines; all fevers are presumed to be due to malaria and chloroquine is given as presumptive treatment. This results in overtreatment. We did a pilot study to see whether some clinical predictors of malaria could be identified in the Indian setting. This case control study was done in a secondary level hospital. All those with fever who were smear positive for malaria were enrolled as cases and other patients fever who were smear negative for malaria served as the controls. All the factors under study were ascertained by a history or detailed clinical examination. A total of 41 cases and 95 controls were enrolled. Of the 41 cases, 35 were positive for P. vivax and six were positive for P. falciparum. After multivariate analysis, only splenomegaly (OR = 2.11; 95% CI = 1.27-3.50) and pallor (OR = 2.01; 95% CI = 1.16-3.48) were significantly associated with malaria. It appears that history of fever along with one or both of these two signs can be a useful predictor of malaria in a secondary level hospital in India. The utility and feasibility of a similar approach in a field setting needs to be studied further.     

Application of the ParaSight-F dipstick test for malaria diagnosis in a district control program

A rapid test for the diagnosis of Plasmodium falciparum infections based on the detection of histidine-rich-protein II, the ParaSight-F test, was evaluated after introduction in a district malaria control program in Uganda. Suspected treatment failures, pregnant women and infants with clinical malaria and general fever cases were tested at health facilities in malaria hypo-, meso- and holoendemic areas. A total of 1326 tests were carried out by health unit staff, cross read by experienced laboratory staff and results compared with thick film microscopy as the standard. Rater agreement in reading the dipstick result between health unit staff and laboratory staff was high, kappa index 0.94 (0.88-0.99). Sensitivity was 99.6% (99.0-100) for parasite densities above 500/microl, 98.6% (97.7-99.6) for densities above 50/microl and 22.2% (8.6-42.3) for densities below 10/microl. With the applied testing strategies no differences were found between endemicity levels or patient categories. Specificity was 86.2% (83.3-88.8) overall, but significantly higher in general fever cases (92.7%) compared to the other patient groups (84.3%, P=0.009). At the given prevalences positive predictive values (ppv) were above 80% and negative predictive values (npv) above 90% in all cases except in pregnant women (ppv: 77.8%). We conclude that in certain situations this test is an alternative to microscopy to improve diagnostic facilities for case management in malaria control programs in endemic African countries.     

Complicated malaria and other severe febrile illness in a pediatric ward in Libreville, Gabon

ABSTRACT: BACKGROUND: Although a substantial decline of Plasmodium falciparum infection is observed in Africa following implementation of new control strategies, malaria is still considered as the major cause of febrile illness in hospitalized African children. The present study was designed to assess the management of febrile illness and to determine the proportion of children with febrile illness hospitalized for primary diagnosis of malaria who had confirmed complicated malaria after implementation of new malaria control strategies in Libreville, Gabon. METHODS: Demographic, clinical and biological data from hospitalized children with fever or a history of fever with a primary diagnosis of clinical malaria, aged less than 18 years old, who benefited from hematological measurements and microscopic malaria diagnosis were recorded and analyzed during a prospective and observational study conducted in 2008 in the Centre Hospitalier de Libreville. RESULTS: A total of 418 febrile children were admitted at hospital as malaria cases. Majority of them (79.4%) were aged below five years. After medical examination, 168 were diagnosed and treated as clinical malaria and, among them, only 56.7% (n = 95) had Plasmodium falciparum positive blood smears. Age above five years, pallor, Blantyre Coma Score <=2 and thrombocytopenia were predictive of malaria infection. Respiratory tract infections was the first leading cause of hospitalization (41.1%), followed by malaria (22.7%); co-morbidities were frequent (22%). Less than 5% of suspected bacterial infections were confirmed by culture. Global case fatality rate was 2.1% and 1% for malaria. Almost half (46%) of the children who received antimalarial therapy had negative blood smears. Likewise, antibiotics were frequently prescribed without bacteriological confirmation. CONCLUSIONS: The use of clinical symptoms for the management of children febrile illness is frequent in Gabon. Information, training of health workers and strengthening of diagnosis tools are necessary to improve febrile children care.     

Perception of chloroquine efficacy and alternative treatments for uncomplicated malaria in children in a holoendemic area of Tanzania: implications for the change of treatment policy

Prior to policy change from chloroquine (CQ) to sulphadoxine/pyrimethamine (S/P; Fansidar) we assessed the perception of CQ efficacy and the alternative treatment options for malaria in children among parents/guardians (N=527) of under-fives attending first level health facilities on account of fever. It was hypothesized that the long experience with CQ and its antipyretic effect (lacking in S/P) might impede acceptance of S/P for wider use as first-line drug. Malarial fevers in children were most commonly treated with CQ (92.8%), followed by quinine (60.7%) and S/P (28.7%). A 63.2% knew the reasons for non-response to antimalarial treatment, and only 50% were aware that CQ could fail to treat malaria, and 57.1% knew alternative treatment options, namely quinine (52.2%) and S/P (20.5%). Generally, decreased efficacy of CQ had been noticed, and quinine was prescribed for both suspected and proven CQ failures in first level health facilities and the district hospital. S/P was judged to be more effective than quinine, but too strong for children, and was the least known drug in the study area. All formulations of S/P cost more per dose for a child and an adult than CQ. The implications of these findings on the change of malaria treatment policy are discussed.     

Nonmalarial acute undifferentiated fever in a rural hospital in central India: diagnostic uncertainty and overtreatment with antimalarial agents

Nonmalarial acute undifferentiated fever (NMAUF) refers to a febrile illness with no indication of an organ-specific disease after diagnosis of malaria has been excluded. In developing countries, the empirical treatment of NMAUFs with antimalarial drugs continues even in the era of highly specific rapid diagnostic tests (RDTs) for malaria. We carried out a retrospective review of patients with fever admitted to a rural teaching hospital in central India. We categorized patients with NMAUF into different clinical syndromes and determined their demographic profile, inhospital course, and the pattern of antimalarial use. The study sample included 1,197 adult patients who were investigated for malaria; 1,053 (88%) of them had NMAUF, and use of further diagnostics in this group was limited. Despite one or more negative tests for malaria, many patients (39.9%, 95% CI 37.0-43.3) received antimalarial drugs. These results suggest a need for guidelines and training to improve empirical treatment of NMAUF.     

Malaria dipsticks beneficial for IMCI in Cambodia

OBJECTIVES: The Integrated Management of Childhood Illness (IMCI) approach and new clinical treatment guidelines to control malaria among children less than 5 years old were introduced recently in Cambodia. This study was conducted to finalize the malaria part of the national IMCI fever chart. METHODS: A total of 323 sick children 2-59 months old were studied at rural health centres in northern Cambodia from February to April 2000. Cases with fever (by axillary temperature or history) or anaemia (by palmar pallor) were tested with dipsticks for Plasmodium falciparum and Plasmodium vivax in high and low malaria risk areas and, if positive, treated with anti-malarials. RESULTS: The draft IMCI chart identified children with malaria safely and effectively (sensitivity 14 of 15, approximately 93% and specificity 292 of 308, approximately 95%). The study confirmed the potential of malaria dipsticks as a part of IMCI case management. CONCLUSION: The Cambodian Ministry of Health will use the studied malaria chart during the Early Implementation Phase of IMCI. Dipsticks able to detect P. falciparum and P. vivax with high sensitivity and acceptable cost will be needed for this purpose. To promote the rational use of dipsticks, the National Centre for Malaria Control, Parasitology and Entomology (Centre National de Malaridogie, Parasitologie et Entomologie, CNM) should list all known malaria risk areas in the country and prepare detailed local maps guiding case management especially in transitional zones.     

Malaria morbidity,treatment-seeking behaviour,and mortality in a cohort of young children in rural Burkina Faso

OBJECTIVE: To describe the pattern of fever-associated morbidity, treatment-seeking behaviour for fever episodes, and cause-specific mortality in young children of a malaria-holoendemic area in rural Burkina Faso. METHODS: In a longitudinal community-based intervention study, 709 representative children aged 6-31 months were followed daily over 6 months (including the main malaria transmission period) through village-based field staff. RESULTS: Of 1848 disease episodes, 1640 (89%) were fever episodes, and of those, 894 (55%) were attributed to malaria (fever + > or =5000 parasites/microl). Eighty-five percent of fever episodes were treated, mainly with chloroquine and paracetamol, 69% of treatments took place in households, 16% in local health centres, 13% in villages, and 1% in hospitals. Treatment-seeking in a health centre or hospital was associated with accessibility and disease severity. Cerebral malaria and malnutrition-associated diarrhoea were the most frequently diagnosed causes of death. While most children with a post-mortem diagnosis of diarrhoea had not received any treatment, children who died of malaria had often received insufficient treatment. In particular, there was a lack of an appropriate second-line treatment at formal health services after chloroquine treatment had failed to resolve symptoms. CONCLUSIONS: These findings call for more effective prevention and treatment of malaria, malnutrition and diarrhoea in rural African communities, as well as for better supervision of existing malaria treatment guidelines in formal health services.     

Community participation in malaria surveillance and treatment. II. Evaluation of the volunteer collaborator Network of Guatemala.

To evaluate the effectiveness of the Volunteer Collaborator Network (VCN) of Latin America as a community-based malaria case detection and treatment system, we conducted a study of the VCN of Guatemala. Volunteer Collaborators took 72.6% of all blood smears and identified 81.3% of all malaria cases reported by the Guatemalan National Malaria Service. The average volunteer treated 5.8 patients per month (range 0-32.8). In contrast, passive case detection (PCD) posts in government hospitals and health centers treated an average of 12.5 patients per month (range 0.5-91.4). The slide positivity rate of blood smears taken by Volunteer Collaborators was 16.2% compared with 9.7% for PCD posts in health centers and 10.3% for malaria workers during active case detection. The average delay between the date a blood smear was taken and examined ranged from 18.1 days on the Pacific coastal plain to 26.3 days in the less accessible northern region of the country. An additional 14.5 to 47.6 days elapsed before the radical treatments were initiated in these two regions. Seventy percent of the patients completed their radical treatments. In a survey conducted on the Pacific coastal plain of Guatemala, of 1,021 patients with chills and/or fever who believed they had malaria, 20.0% had visited a Volunteer Collaborator and 4.9% were treated at a government health center. Thus, the PCD network detected only 25% of all patients with symptoms suggestive of malaria. Most of the remaining patients treated themselves with antimalarial medications purchased in stores and pharmacies, but less than 15% of these patients used adequate courses of therapy. Furthermore, the rate of detection of symptomatic patients with malaria varied considerably from one community to another. Thus, data from the VCN are probably most useful when groups of communities or geographic areas are stratified for malaria control activities because at this level, variations between individual Volunteer Collaborator posts will be minimized. In spite of these problems, the VCN remains an excellent source of epidemiologic data for malaria control programs and the most practical means available for providing timely, appropriate antimalarial therapy to febrile patients in rural areas.     

Individual risk factors for Plasmodium vivax infection in the residual malaria transmission focus of Oaxaca, Mexico

OBJECTIVE: To identify individual risk factors for malaria infection of inhabitants in the residual transmission focus on the Pacific coast of Oaxaca, Mexico. MATERIALS AND METHODS: A population-based, matched case-control study was conducted from January 2002 to July 2003 comparing the frequency of exposure to individual risk factors in subjects presenting clinical malaria and uninfected controls. A malaria case was defined as an individual living in the study area presenting malaria symptoms and a Plasmodium vivax-positive thick blood smear; controls were individuals negative to P. vivax parasites and antibodies of the same gender and with +/- five years as the case. A standardized questionnaire was used to record information about the individual risk factors associated with malaria episodes in cases and two controls for each case. RESULTS: In a multiple conditional logistic regression model analysis of data from 119 cases and 238 controls, 18 out of 99 variables were significantly associated (p< 0.05) with increased risk of malaria, including: being born in another locality (RM 3.16, 95% IC 1.16-6.13); speaking only an autochthonous language (RM= 2.48, 95% IC 1.19-3.77); having poor knowledge about malaria (RM= 2.26 95% IC 1.10-4.66 P< 0.02); the amount of vegetation around the house (RM= 20.43, 95% IC 5.98-70.87, P< 0.000; RM= 3.78, 95% IC 1.21-11.80, for 60-100% and 30-59%, respectively); living in houses constructed with perishable materials (RM= 2.85, 95% IC 1.62-5.01); living on the periphery of the town (RM= 6.23, 95% IC 3.50-11.0); sleeping on a dirt floor (RM= 2.98, 95% IC 1.78-5.01) or with two or more people in the same bed (RM= 1.85, 95% CI 1.09-3.14); not using bed nets (RM= 2.39, 95% IC 1.18-4.83, P< 0.003) or using bed nets with holes (RM= 13.93, 95 IC 2.48-78.01); traveling outside of the village (RM= 9.16, 95% IC 1.98-42.2); and previous malaria cases in the house (RM= 5.84, 95% IC 3.33-10.22). CONCLUSIONS: Risk of malaria infection was associated with socio-cultural and environmental factors exposing individuals to mosquito bites. A higher risk of malaria infection occurred outside the locality and by intradomiciliar transmission probably as a result of relapsing asymptomatic relatives.