During the 10 months of implementation, 30,195 patients were seen at the 12 health facilities. Among all patients seen, 15,043 (49.8%) were diagnosed with malaria (clinical or laboratory-confirmed diagnosis). Among those with a malaria diagnosis, 9,292 (61.8%) were children less than 5 years of age, and 5,751 (38.2%) were adults and children aged 5 and older. Among 10,737 patients tested with RDTs, test results were recorded for 10,650 (99.2%) patients. Age was recorded for 10,599 (99.5%) of patients with test results, and among them 284 (2.7%) were less than 5 years of age, and 10,315 (97.3%) were aged 5 and older. Overall RDT sensitivity was 90.7% (range by facility 85.7–96.5%) and specificity was 73.5% (range by facility 50.0–84.3%) compared with reference microscopy. When the 44 positive blood smears with parasite densities less than 200 parasites/µL are excluded, sensitivity and specificity increase to 91.1% and 77.9%, respectively. shows monthly RDT sensitivity and specificity, and the percentage of positive RDTs and positive blood smears.
Sensitivity, specificity, and percent positive blood smear of rapid diagnostic tests (RDTs) by month, Rufiji District, Tanzania, December 2007–October 2008.
also illustrates that there was a seasonal increase in the percentage of positive blood smears following the rainy season from April to July. Blood smear results were available for 3,914 patients, of which 40.1% (1,577/3,914) were positive for P. falciparum malaria. No non-falciparum species were identified by the reference microscopists. The percentage of positive blood smears ranged from a low of 14.4% in December 2007 to a high of 60.5% in June 2008, the peak of transmission. The same seasonal increase seen in blood smears is reflected in the percentage of positive RDTs, which ranged from a low of 22.3% in December 2007 to a high of 72.4% in June 2008. Sensitivity of RDTs increased with increasing parasite density (). Sensitivity for detection of parasite densities below the 200 parasites/µL was 79.5%, and decreased slightly to 72.0% for parasite densities of the 200 to 800 parasites/µL. Thereafter, RDT sensitivity increased with increasing parasite density and the overall trend was statistically significant (P < 0.001). The predictive value of a positive test was 73.0% with a false positive rate of 26.5%. The predictive value of a negative test was 93.0% with a false negative rate of 9.3%.
Rapid diagnostic test (RDT) sensitivity by parasite density, Rufiji District, Tanzania, December 2007–October 2008 (3,914 blood smears reviewed, 1,577 positive blood smears)
Patients were also queried about recent use of antimalarial drugs. All tested patients were asked if they had received treatment of malaria in the 3 weeks before being tested. Health workers were instructed to refer patients who had recently been treated for malaria to the nearest referral health facility; however, 585 patients who had received recent treatment with antimalarials were tested with RDTs. Among these 585 patients 454 (78.8%) had a positive RDT result. One hundred forty-nine (25.5%) patients who had recently received treatment also had a blood smear taken for QA. Among these 149, 104 (69.8%) had positive blood smears and 45 (30.2%) had negative blood smears. One hundred (96.2%) of the 104 recently treated patients with positive blood smears had positive RDT results. Twenty-two (48.9%) of the 45 recently treated patients with negative blood smears had false positive RDT results.
There was a high degree of concordance among blood smear and RDT results. Among 3,914 blood smears read by the reference microscopists there were 1,431 true positive and 1,820 true negative RDT results, for 3,251 (83.1%) concordant results. Of the 663 discordant results, 517 (78.0%) were false positives and 146 (22.0%) were false negatives according to reference microscopy. Three hundred forty-five (52.0%) blood smears were reviewed by a second microscopist, and 159 were reviewed by a third reader. Approximately half of the discordant slides were not available for second or third readings because they were lost or damaged in transport. When unavailable for review the first microscopist's reading was kept, as this allowed the most conservative estimation of sensitivity and specificity. Among the 345 blood smears reviewed, there was agreement between the first and second readers on 260 (75.4%). Of the 85 (24.6%) blood smears with discordant readings between the first and second microscopists, a third reader reviewed 51 (60.0%). The third reader agreed with the first microscopist on 7 (13.7%) slides and agreed with the second microscopist on 44 (86.3%) slides.
Temperature was recorded weekly in the area of the health facilities where RDTs were stored. The average temperature recorded during the study period was 31.7°C (range 23–37°C).