Plasmodium DNA contamination between blood smears during Giemsa staining and microscopic examination

Giemsa-stained blood smears are mainly used for microscopic examination to diagnose malaria. However, they may also be subjected to polymerase chain reaction (PCR) to confirm diagnosis or for retrospective studies requiring the analysis of old smears. We investigated the possibility of DNA contamination occurring during automated Giemsa staining or due to the failure to clean the oil-immersion objective during microscopic examination. We tested blood smears from uninfected, Plasmodium vivax-infected, and P. falciparum-infected patients. DNA contamination was observed after both staining and microscopy, although contamination was unpredictable during staining. These results are of utmost importance when smears are used for PCR.