Ers that is attributable to CP21 malaria is very low: only 3.2 [3]. The presence of vomiting slightly increases the probability of disease, but that of cough has the opposite effect (unpublished data). If the threshold of 1.1 is considered, then the nurse should treat, that is the right decision according to guidelines. The threshold based on mortality only, without costs, is even lower, then the decision would be the same. If a RDT is available, the probability of disease remains over the test/treatment threshold, considering costs or not : therefore, presumptive treatment remains the elective option. Case 2. At mid- October an 8-month-old girl is taken to the same dispensary with high fever (39uC) and vomiting. She breathes fast (52 respirations per minute). No cough. No clear pathologic finding at the chest auscultation. Again, the nurse should treat for malaria according to guidelines, if no test were available. In the high transmission season, malaria accounts for about two thirds of all fever cases [3]. Moreover, the presence of vomiting further increases the probability of malaria which is obviously much higher than the threshold (of 1.1 or 0.3 considering or not considering costs, respectively). The nurse should treat for malaria. With the availability of a RDT, WHO BMS5 guidelines recommend testing, but the threshold-based analysis shows that the test should not be done, as a negative result would not change the decision to treat. Case 3. In April a 32-year-old local farmer consults for a 2-day fever, a slight headache and some “body pain”. He refers night sweats. The physical examination is normal. Temperature is 37.8uC. Once again, the nurse should treat for malaria according to guidelines, in case no test is available. The probability of clinical malaria (dry season) is 1.7 only [3]. The treatment (or decision) threshold without costs is 7.1 , that based on the upper value attributed to a death averted is over 50 (while with the lower value an adult should never be treated with an ACT). According to the threshold the nurse should refrain from treatment. With an available RDT, the decision would not change in case of positive result, therefore the nurse should not use the test (Figure 6). Without considering costs, the conclusion would be the same.Estimate of the Test and 
Test/Treatment ThresholdEstimate of the test and test/treatment threshold without considering costs. For children, based on previously obtaineddata on test accuracy in the two seasons and on Equations 5 to 8 (calculations shown in Results S1), in the dry season the test threshold would be 0.08 and the test/treatment threshold 3.1 , while in the rainy season they would be 0.2 and 3.2 , respectively. For adults, the test and the test/treatment threshold would be 1.8 and 89.9 in the dry season, while in the rainy season 3 and 60.9 
, respectively. Test and test/treatment threshold including costs. For children in the dry season, the maximal test cost was 0.85 J while the real cost was 0.71 J (calculation shown in Results S1). The test and the test/treatment thresholds were 1.0 and 2.8 . In the rainy season, the maximal test cost was 0.44 J (largely below the real cost of 0.71 J), therefore the test option cannot be considered. For adults in the dry season the maximal test cost was 0.75 J, only slightly over the real cost; the test threshold was 50.6 , and the test/treatment threshold was 54.7 . In the rainy season, the maximal test cost for adults was 0.64 J.Ers that is attributable to malaria is very low: only 3.2 [3]. The presence of vomiting slightly increases the probability of disease, but that of cough has the opposite effect (unpublished data). If the threshold of 1.1 is considered, then the nurse should treat, that is the right decision according to guidelines. The threshold based on mortality only, without costs, is even lower, then the decision would be the same. If a RDT is available, the probability of disease remains over the test/treatment threshold, considering costs or not : therefore, presumptive treatment remains the elective option. Case 2. At mid- October an 8-month-old girl is taken to the same dispensary with high fever (39uC) and vomiting. She breathes fast (52 respirations per minute). No cough. No clear pathologic finding at the chest auscultation. Again, the nurse should treat for malaria according to guidelines, if no test were available. In the high transmission season, malaria accounts for about two thirds of all fever cases [3]. Moreover, the presence of vomiting further increases the probability of malaria which is obviously much higher than the threshold (of 1.1 or 0.3 considering or not considering costs, respectively). The nurse should treat for malaria. With the availability of a RDT, WHO guidelines recommend testing, but the threshold-based analysis shows that the test should not be done, as a negative result would not change the decision to treat. Case 3. In April a 32-year-old local farmer consults for a 2-day fever, a slight headache and some “body pain”. He refers night sweats. The physical examination is normal. Temperature is 37.8uC. Once again, the nurse should treat for malaria according to guidelines, in case no test is available. The probability of clinical malaria (dry season) is 1.7 only [3]. The treatment (or decision) threshold without costs is 7.1 , that based on the upper value attributed to a death averted is over 50 (while with the lower value an adult should never be treated with an ACT). According to the threshold the nurse should refrain from treatment. With an available RDT, the decision would not change in case of positive result, therefore the nurse should not use the test (Figure 6). Without considering costs, the conclusion would be the same.Estimate of the Test and Test/Treatment ThresholdEstimate of the test and test/treatment threshold without considering costs. For children, based on previously obtaineddata on test accuracy in the two seasons and on Equations 5 to 8 (calculations shown in Results S1), in the dry season the test threshold would be 0.08 and the test/treatment threshold 3.1 , while in the rainy season they would be 0.2 and 3.2 , respectively. For adults, the test and the test/treatment threshold would be 1.8 and 89.9 in the dry season, while in the rainy season 3 and 60.9 , respectively. Test and test/treatment threshold including costs. For children in the dry season, the maximal test cost was 0.85 J while the real cost was 0.71 J (calculation shown in Results S1). The test and the test/treatment thresholds were 1.0 and 2.8 . In the rainy season, the maximal test cost was 0.44 J (largely below the real cost of 0.71 J), therefore the test option cannot be considered. For adults in the dry season the maximal test cost was 0.75 J, only slightly over the real cost; the test threshold was 50.6 , and the test/treatment threshold was 54.7 . In the rainy season, the maximal test cost for adults was 0.64 J.
