METHODS: In total, 153 patients with confirmed coronavirus disease 2019 (COVID-19) who had been admitted to the regional referral hospital or who self-isolated at home were included in this study. Nasopharyngeal swab specimens and saliva samples were collected on the same day, and were tested for SARS-CoV-2 infection using reverse transcriptase polymerase chain reaction.

RESULTS: The sensitivity and specificity of saliva samples were 81.5% and 76.4%, respectively, in cases that had been confirmed as COVID-19 using nasopharyngeal swab samples. Positive predictive values and negative predictive values were 92.3% and 54.1%, respectively. The highest detection rates were found among samples collected 4-7 days since symptom onset.

METHODS: A cross-sectional survey was conducted in six villages in Langkat district, North Sumatera Province in June 2019. Data were recorded using a standardized questionnaire. Finger pricked blood samples were obtained for malaria examination using rapid diagnostic test, thick and thin blood smears, and polymerase chain reaction.

RESULTS: A total of 342 individuals were included in the study. Of them, one (0.3%) had a microscopic Plasmodium malariae infection, no positive RDT examination, and three (0.9%) were positive for P. malariae (n = 1) and Plasmodium knowlesi (n = 2). The distribution of bed net ownership was owned by 40% of the study participants. The participants had a house within a radius of 100-500 m from the forest (86.3%) and had the housing material of cement floor (56.1%), a tin roof (82.2%), wooden wall (35.7%), bamboo wall (28.1%), and brick wall (21.6%).

METHODS: A cross-sectional survey was conducted in Langkat district, North Sumatera Province, in June 2019. Basic demographic data and filter paper blood spots were collected from 339 participants. Antibody responses to two P. falciparum (PfAMA-1 and PfMSP-119) and two P. vivax (PvAMA-1 and PvMSP-119) antigens were measured using indirect enzyme-linked immunosorbent assay (ELISA). Seroconversion rates (SCR) were estimated by fitting a simple reversible catalytic model to seroprevalence data for each antibody. Multiple logistic regression was used to investigate factors associated with exposure.

RESULTS: The overall malaria seroprevalence was 10.6% for PfAMA-1, 13% for PfMSP-119, 18.6% for PvAMA-1, and 7.4% for PvMSP-119. Seropositive individuals for P. falciparum (PfAMA-1/PfMSP-119) and P. vivax (PvAMA-1/PvMSP-119) were similar at 20.7%, with no significant differences observed between age groups (p > 0.05). Based on the reversible catalytic model, the calculated SCRs indicated a higher level of P. falciparum transmission than P. vivax using all tested antigens. In the adjusted model, only spending nights in the forest was associated with P. vivax seropositivity (odd ratio: 3.93, p < 0.001).

METHODOLOGY/PRINCIPAL FINDINGS: An established ultra-sensitive Plasmodium genus quantitative-PCR (qPCR) assay targeting the 18S rRNA gene underwent LOD evaluation with and without reverse transcription (RT) for P. knowlesi, P. cynomolgi and P. vivax using total nucleic acid preserved (DNA/RNA Shield) isolates and archived dried blood spots (DBS). LODs for selected P. knowlesi-specific assays, and reference P. vivax- and P. cynomolgi-specific assays were determined with reverse transcription (RT). Assay specificities were assessed using clinical malaria samples and malaria-negative controls. The use of reverse transcription improved Plasmodium species detection by up to 10,000-fold (Plasmodium genus), 2759-fold (P. knowlesi) and 1000-fold (P. vivax and P. cynomolgi). The Kamau et al. Plasmodium genus RT-qPCR assay was highly sensitive for P. knowlesi detection with a median LOD of ≤0.0002 parasites/μL compared to 0.002 parasites/μL for P. cynomolgi and P. vivax. The LODs with RT for P. knowlesi-specific PCRs were enhanced for the Imwong et al. 18S rRNA (0.0007 parasites/μL) and Divis et al. real-time 18S rRNA (0.0002 parasites/μL) assays, but not for the Lubis et al. hemi-nested SICAvar (1.1 parasites/μL) and Lee et al. nested 18S rRNA (11 parasites/μL). The LOD for P. vivax- and P. cynomolgi-specific assays with RT were moderately improved at 0.02 and 0.002 parasites/μL, respectively (1000-fold change). For DBS P. knowlesi samples the use of RT also markedly improved the Plasmodium genus qPCR LOD from 19.89 to 0.08 parasites/μL (249-fold change); no LOD improvement was demonstrated in DBS archived beyond 6 years. The Plasmodium genus and P. knowlesi-assays were 100% specific for Plasmodium species and P. knowlesi detection, respectively, from 190 clinical infections and 48 healthy controls. Reference P. vivax-specific primers demonstrated known cross-reactivity with P. cynomolgi.