The reliability of the microscopic diagnosis of malaria in the field and in the laboratory.

Four hundred and seventy thick and thin blood films were prepared from 129 villagers in the Solomon Islands. After staining with Giemsa, Leishman's, and Field's stains, they were randomized and examined in the field, using a miniature McArthur microscope. The specimens were then examined in the local central laboratory and by a microbiologist at a hospital in England. Films over which there was disagreement were examined by an expert at the Liverpool School of Tropical Medicine. The rate of false negative diagnoses (for thick films) was 3% for the field worker, 9% for the malaria laboratory, and 27% for the English hospital. Field diagnosis was no less reliable than laboratory diagnosis (P less than 0.001). Field's stain was the most reliable stain for both thick films (P less than 0.001) and thin films (P less than 0.05), for which a new staining technique is described.