Hoang Lan Phuong

Seroprevalence of dengue antibodies, annual incidence and risk factors among children in southern Vietnam

Dengue is highly endemic in southern Vietnam and all four serotypes of dengue virus have already been identified. To determine the age‐specific prevalence of dengue and associated risk factors, we conducted a serological study at two primary schools and assessed risk factors by analysing childrens questionnaires and household surveys. Sera were collected from 961 primary schoolchildren in Binh Thuan Province and tested for the presence of dengue virus serum antibodies using an indirect immunoglobulin G (IgG) enzyme‐linked immunosorbent assay (ELISA). The antibody prevalence of the total population was 65.7% (n = 631) which increased from 53.0 to 88.2% with age. The annual incidence of a first dengue infection, estimated by binary regression of the seroprevalence by age, was 11.7%. Interestingly, the prevalence of dengue IgG antibodies was significantly higher in children who confirmed using a pit latrine (RR 1.467, 95% CI: 1.245–1.730) and whose domestic environment contained discarded cans (RR 1.238, 95% CI: 1.042–1.470) and pigs (RR 1.228, 95% CI: 1.002–1.504). The epidemiology of dengue in southern Vietnam is stable with a constantly high annual incidence of first infections. Transmission occurs mainly peri‐domestically, which has important public health implications.

Pharmacokinetics and pharmacodynamics of intravenous artesunate in severe falciparum malaria.

ABSTRACT To provide novel data relating to the dispositions, effects, and toxicities of the artemisinin derivatives in severe malaria, we studied 30 Vietnamese adults with slide-positive falciparum malaria treated with intravenous artesunate. Twelve patients with complications (severe; group 1) and 8 patients without complications but requiring parenteral therapy (moderately severe; group 2) received 120 mg of artesunate by injection, and 10 patients with moderately severe complications (group 3) were given 240 mg by infusion. Serial concentrations of artesunate and its active metabolite dihydroartemisinin in plasma were measured by high-performance liquid chromatography. The time to 50% parasite clearance (PCT50) was determined from serial parasite densities. Full clinical (including neurological) assessments were performed at least daily. In noncompartmental pharmacokinetic analyses, group mean artesunate half-lives (t1/2) were short (range, 2.3 to 4.3 min). The dihydroartemisinin t1/2 (range, 40 to 64 min), clearance (range, 0.73 to 1.01 liters/h/kg), and volume of distribution (range, 0.77 to 1.01 liters/kg) were also similar both across the three patient groups (P > 0.1) and to previously reported values for patients with uncomplicated malaria. Parasite clearance was prompt (group median PCT50 range 6 to 9 h) and clinical recovery was complete under all three regimens. These data indicate that the pharmacokinetics of artesunate and dihydroartemisinin are not influenced by the severity of malaria. Since the pharmacokinetic parameters for both artesunate and dihydroartemisinin were similar regardless of whether injection or infusion was used, artesunate can be considered a prodrug that is converted stoichiometrically to dhydroartemisinin. Conventional doses of artesunate are safe and effective when given to patients with complications of falciparum malaria.

Penetration of Dihydroartemisinin into Cerebrospinal Fluid after Administration of Intravenous Artesunate in Severe Falciparum Malaria

ABSTRACT Penetration of cerebrospinal fluid (CSF) by artesunate and DHA was assessed in six adults with cerebral or severe malaria. Lumbar punctures were performed on admission and during convalescence, at 15 min (patient 1), 30 min (patient 2), 45 min (patient 3), 60 min (patient 4), 90 min (patient 5), and 120 min (patient 6) after intravenous administration of 120 mg of artesunate. No artesunate was detectable in CSF. In both studies, DHA levels in CSF increased with time while dihydroartemisinin levels in plasma fell. Dihydroartemisinin might accumulate in CSF during frequent artesunate dosing.

Seroepidemiology of leptospirosis in southern Vietnamese children.

Objective  To estimate the seroprevalence of human leptospirosis in southern Vietnam.

Evaluation of Two Rapid Immunochromatographic Assays for Diagnosis of Dengue among Vietnamese Febrile Patients

ABSTRACT Results from two dengue rapid tests, the PanBio Duo cassette and the SD Bioline strip test, were compared to those of enzyme-linked immunosorbent assays (Focus Diagnostics) from sera of 200 Vietnamese febrile patients. The PanBio assay was superior, with sensitivity and specificity values for acute-phase serum samples of 54% and 70% (immunoglobulin M) and 70% and 88% (immunoglobulin G), respectively.

Detection of dengue nonstructural 1 (NS1) protein in Vietnamese patients with fever

Diagnosing dengue in febrile patients is challenging. Of a total of 459 patients with acute undifferentiated fever, randomly selected from 12 primary health facilities and 1 clinic of the provincial malaria station in southern Vietnam, dengue-specific antibody (Ab) and NS1Ag enzyme-linked immunosorbent assay (ELISA) (Platelia, Bio-Rad Laboratories, Hercules, CA 94547, US) were performed on acute (t0) and convalescent (t3 weeks) sera. Polymerase chain reaction (PCR) was used for confirmation. Based on a composite of the NS1Ag-ELISA, Ab-ELISA, and PCR results, 54 (12%) patients had acute dengue. Positive and negative predictive values were 65% and 98% for the Ab-based diagnosis and 91% and 92% for NS1Ag, respectively. The agreement between Ab- and NS1Ag-based diagnosis was poor (kappa value, 0.2). Two patients without dengue had detectable NS1Ag on t0 and t3, 1 just above the cutoff value and 1 with very high values. For 5 dengue patients, NS1Ag was still detectable at very high levels at t3. Dengue NS1Ag can be used for early diagnosis of dengue; infrequent false-positive results need further clarification.

Seroepidemiology and serological follow-up of anti-leptospiral IgG in children in Southern Vietnam

A follow-up study was conducted with 23 months interval to investigate the seroepidemiology and persistence of Leptospira IgG antibodies among healthy children in Binh Thuan province, Southern Vietnam. Sera from 262 children (7-13 years of age) were collected and analysed with a commercially available enzyme-linked immunosorbent assay (ELISA) for Leptospira IgG. Seroconversion was observed in 10.4% (22 of 211, 95% CI: 5.6-26.7) of the children, of whom 18 (8.5%) had probably and four (1.9%) had certainly been exposed to Leptospira. Based on the reduction of sero-negatives of 1.9% among children who have been certainly exposed, the annual seroconversion rate, a measure of the incidence rate of Leptospira infections, corresponds to 0.99% (95% CI: 0.39-2.52). In 61% (31 of 51, 95% CI: 47.1-73.0) of the children with past-infection, Leptospira IgG antibodies remain detectable after 2 years. Data from this study indicate that IgG antibody responses against Leptospira may persist at least for 2 years in children without manifestations of leptospirosis. Results of study uncover the true incidence of leptospirosis infection, the dynamics of waxing and waning antibody concentrations and points at a larger burden of clinically non-significant Leptospira infections in Southern Vietnam. This also indicates background reactivity for serological testing and thus serological result of a single serum sample must be carefully interpreted.