Risk factors of chloroquine resistance in Plasmodium falciparum malaria

Objective: To identify patient-related risk factors of chloroquine resistance. Design: A case control study. Subjects: Plasmodium falciparum infected school children were followed prospectively for 7 days for the detection of chloroquine resistance. Cases were 38 individuals with chloroquine resistant infections. Controls were 125 individuals with chloroquine sensitive infections. Cases were compared with controls with respect to previous or current study factor levels. Subjects were recruited from randomly selected schools which were stratified for area. Study location was in North Guadalcanal, Solomon Islands. Outcome measure: Treatment failure of chloroquine in standard dosage (25 mg/kg). Follow-up period was 7 days. Results: Logistic regression resulted in 5 independent significant predictors of chloroquine resistance, obtained simultaneously with the diagnosis of malarial infection: (i) Young age (odds ratio (OR) for age < 7 years: 7.1; 95% confidence interval (CI): 2.5–25.0; OR per year increase after the age of 5 years: 0.8; 95% CI: 0.6–0.9). (ii) High parasite density (OR for > 1000/gml: 5.0; 95% CI: 2.0–10.6; OR per 500 parasites/μl increase: 1.3; 95% CI: 1.1–1.7). (iii) Normal spleen size (OR: 4.0; 95% CI: 1.5–10.8). (iv) Malnutrition (OR: 4.9; 95% CI: 1.8–13.2). (v) Presence of gametocytes in the thick smear (OR: 3.0; 95% CI: 1.1–8.0). Conclusion: The identified risk factors are easily measurable without special equipment. They may be useful for health workers in the Solomon Islands, even in remote areas, to identify Plasmodium falciparum infected individuals at high risk for chloroquine resistance before a treatment decision is made.