Association between subclass-specific antibodies against merozoite antigens and P. falciparum blood-stage infections of different densities. Values represent HRs ± 95% confidence intervals. Filled circles, IgG1; open circles, IgG3. PCR, P. falciparum infection determined by PCR; LM, P. falciparum infection determined by light microscopy; >500/μl, P. falciparum infection with a density of >500 parasites/μl; >5000/μl, P. falciparum infection with a density of >5,000 parasites/μl. The 3D7 allele was used for each antigen.