Is Serial Testing Required to Diagnose Imported Malaria in the Era of Rapid Diagnostic Tests?

Abstract

Abstract. Exclusion of malaria traditionally requires three negative serial thick and thin blood films. However, many clinical laboratories now routinely perform rapid diagnostic tests (RDTs) in addition to blood films when malaria is suspected. We sought to determine whether serial testing is necessary in this setting. We examined 388 cases of malaria diagnosed during 1999-2010 at three laboratories in Melbourne, Australia. For each case, we ascertained whether the diagnosis was made on initial or follow-up testing. Nine cases (3.5%) were diagnosed after a negative initial blood film and RDT: 7 Plasmodium vivax, 1 P. ovale, and 1 P. falciparum. Of four case-patients with P. vivax in which clinical data were available, all had recent exposure to antimalarial medication. Our data suggest that among patients who have not received recent anti-malarial therapy, and when RDTs are performed and blood films are prepared, most malaria diagnoses are made by using the first set of tests.

Feasibility and Clinical Outcomes When Using Practice Guidelines for Evaluation of Fever in Returning Travelers and Migrants: A Validation Study

“…Some of the observed diversions, such as not repeating a malaria test when there is no alternative diagnosis, may appear as a clear mismanagement. However, recent studies 19,20 show that very few malaria cases are picked up by a second test. This recommendation might need to be reviewed in the future, especially if two malaria tests (microscopy and rapid diagnostic tests) are performed at first visit.…”

How to interpret malaria tests

“…This is especially true in cases of suspected P. falciparum in a non-immune patient who has not received any treatment 18. The most obvious criticism here is that it is difficult to extrapolate adult data and draw conclusions relating to children.…”

“…The study that looked at ruling out malaria with a single film and a single RDT was done in adults 18. Currently, no similar study looking at this in children exists, which would be useful when thinking about diagnosis in childhood imported malaria.…”

The utility of serial blood film testing for the diagnosis of malaria

“…These invade hepatocytes where they mature into schizonts. 6 The parasite may be in a phase of its life cycle where blood levels may be too low to be detected. The different species of Plasmodium develop in the erythrocytes at different rates and rupture to release waves of new merozoites that re-invade circulating erythrocytes.…”

“…The hepatocytes rupture and release merozoites that invade circulating erythrotyes. 6 This study was carried out in Melbourne, Australia, a non-malaria endemic region where all cases of malaria are imported from overseas. The asexual blood cycle repeats every 24 (P. knowlesi), 48 (P. falciparum, P. vivax, P. ovale) or 72 (P. malariae) hours.…”