How well do malaria tests correlate with disease severity? Comparison of parasite density in children with mild and severe malaria.

BACKGROUND

Accurate diagnosis of malaria is key to proper management and control and an ideal diagnostic parameter that correlates to disease outcome is required. The former would be helpful in correctly identifying patients that need hospitalisation versus those that can be managed at home. This study determined how well the density estimates by microscopy, qPCR and HRP-2 correlate to malaria severity.

MATERIALS AND METHODS

Patients aged ≤ 5 yrs with severe (n = 60, Hb ≤ 6 g/dl) and mild (n = 60, Hb > 6 g/dl) malaria were enrolled to take part in a case control study at Kisumu District Hospital, Western Kenya. Parasite load was determined by microscopy, qPCR targeting the rRNA gene and HRP-2 antigen ELISA.

RESULTS

The median parasite load and the 25 and the 75 percentile by microscopy in children with severe malaria (SM) was 49,958 parasites/μl (12,013-128,695) compared to 24,233 (6,122-103,886) in the group with mild malaria (MM), P = 0.10. By qPCR, the translated median parasite density was 31,550 parasites/μl (4,106-196,640) in the SM group compared to 24,365 parasites/μl (5,512-93,401) in the MM group (P = 0.73). According to HRP-2, the translated median parasite load in children with SM was 628,775 parasites/μl (332,222-1.165x106) compared to 150,453 (94,292-399,100) in children with MM (P < 0.0001).

CONCLUSIONS

Unlike microscopy and qPCR, the parasite load detected by HRP-2 correlates with disease severity. Because of its unique attributes, HRP-2 is able to account for trophozoites and schizonts that are sequestered away from peripheral circulation. Because it persists in circulation, it also serves as an indicator of the magnitude of current and recent infections.