Editor—The methods applied to enhance the interpretation of the data by Plowe et al deserve comment.1
The World Health Organization has developed several standardised protocols to assess the efficacy of antimalarial drugs, which are intended to determine treatment failures and not resistance patterns of the parasite. Recently, WHO published a revised protocol, giving clear indications of outcome classifications and the target groups (children under 5 years in intense transmission areas) to be monitored.2 The new classification is appropriate for patients with symptoms and includes not only clinical but also parasitological criteria. It becomes redundant now to report the response based on the 1973 classification. Moreover, examination of WHO's database on antimalarial drug efficacy has shown that early treatment failure corresponds closely to parasitological resistance grade RIII + RII, contradicting the authors' claim that early treatment failure is systematically overestimating the true early failure rate.
A technical meeting convened by WHO's regional office for Africa in Harare in August last year agreed that, in intense transmission areas, asymptomatic parasitological failure (quoted as LPF in the new protocol) should be an additional indicator for the interpretation of the test. It was also agreed that an unacceptable failure rate is reached when clinical failure at day 14 is ≥ 15% and total failure ≥ 25%.2 The authors' data in table 2 show that these thresholds have been reached in Ndirande since 1999.
There is clear evidence that the resistance of Plasmodium falciparum to sulfadoxine-pyrimethamine has increased in Malawi over the past 10 years. According to Plowe et al, resistance to sulfadoxine-pyrimethamine was absent in Malawi in 1990.3 The level of cumulative RI-RII-RIII parasitological failure probably reached a peak in Ndirande in 1999. Similar failure rates with chloroquine in six sites in Malawi led to a policy change in 1993.4
Data on the efficacy of sulfadoxine-pyrimethamine in Malawi are a subject of scientific debate. Behind this debate, there is a real public health issue of delivering fully effective drugs to the population.
Competing interests: None declared.
References
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