Pilot assessment of the sensitivity of the malaria thin film.

Published online

Journal Article

BACKGROUND: Malaria microscopy remains the reference standard for malaria diagnosis in clinical trials (drug and vaccine), new diagnostic evaluation, as well as in clinical care in much of the world today. It is known that microscopy is an imperfect gold standard, and that very low false positive rates can dramatically lower protective efficacy estimates in malaria prevention trials. Although new methods are now available, including malaria rapid diagnostic tests and PCR, neither is as yet validated in the clinical trial setting and both have limitations. Surprisingly, the sensitivity of thin smears is not well established and thin smears are not commonly used in the developing world. METHODS: Malaria thick and thin films were collected in the lowlands of Western Kenya. All had density determined by four readings with two methods, as well as species identified. Thirty-six with low density parasitaemia had the thin smear read by five independent microscopists, two were expert and three were qualified. Microscopists read the entire thin film. For the first 10 parasites seen, they reported the species, appearance, time, field number, and red blood cells in the field. Total parasites, total fields, and total time to examine the smear were also recorded. RESULTS: Median parasitaemia was 201 parasites/mul, mean 1,090 +/- 2,195, range 6-11,124 parasites/mul for the 36 smears evaluated. The data revealed a density dependent increase in sensitivity, with 100% sensitivity achieved at >200 parasites/mul for experts and >500 parasites/mul for qualified readers. Thin film readings confirmed parasitaemia 74% of the time by experts, and 65% of the time for qualified microscopists. The 95th percentile for time to detect parasitaemia was 15 minutes for experts, 17 minutes for qualified microscopists. This decreased to 4-10 minutes for experts at densities of > 200 parasites/mul. Additionally, substantial discordance for species identification was observed. CONCLUSION: The thin film is sensitive enough to be a useful tool to confirm malaria diagnosis in study subjects in some settings. Specificity of the thin film and its utility for confirming thick film or other diagnostic test results should be assessed further.

Full Text

Duke Authors

Cited Authors

  • Ohrt, C; O'Meara, WP; Remich, S; McEvoy, P; Ogutu, B; Mtalib, R; Odera, JS

Published Date

  • January 28, 2008

Published In

Volume / Issue

  • 7 /

Start / End Page

  • 22 -

PubMed ID

  • 18226243

Pubmed Central ID

  • 18226243

Electronic International Standard Serial Number (EISSN)

  • 1475-2875

Digital Object Identifier (DOI)

  • 10.1186/1475-2875-7-22

Language

  • eng

Conference Location

  • England