Last data update: May 06, 2024. (Total: 46732 publications since 2009)
Records 1-2 (of 2 Records) |
Query Trace: Nahlen BL[original query] |
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Serological markers for monitoring historical changes in malaria transmission intensity in a highly endemic region of Western Kenya, 1994-2009
Wong J , Hamel MJ , Drakeley CJ , Kariuki S , Shi YP , Lal AA , Nahlen BL , Bloland PB , Lindblade KA , Were V , Otieno K , Otieno P , Odero C , Slutsker L , Vulule JM , Gimnig JE . Malar J 2014 13 (451) 451 BACKGROUND: Monitoring local malaria transmission intensity is essential for planning evidence-based control strategies and evaluating their impact over time. Anti-malarial antibodies provide information on cumulative exposure and have proven useful, in areas where transmission has dropped to low sustained levels, for retrospectively reconstructing the timing and magnitude of transmission reduction. It is unclear whether serological markers are also informative in high transmission settings, where interventions may reduce transmission, but to a level where considerable exposure continues. METHODS: This study was conducted through ongoing KEMRI and CDC collaboration. Asembo, in Western Kenya, is an area where intense malaria transmission was drastically reduced during a 1997-1999 community-randomized, controlled insecticide-treated net (ITN) trial. Two approaches were taken to reconstruct malaria transmission history during the period from 1994 to 2009. First, point measurements were calculated for seroprevalence, mean antibody titre, and seroconversion rate (SCR) against three Plasmodium falciparum antigens (AMA-1, MSP-119, and CSP) at five time points for comparison against traditional malaria indices (parasite prevalence and entomological inoculation rate). Second, within individual post-ITN years, age-stratified seroprevalence data were analysed retrospectively for an abrupt drop in SCR by fitting alternative reversible catalytic conversion models that allowed for change in SCR. RESULTS: Generally, point measurements of seroprevalence, antibody titres and SCR produced consistent patterns indicating that a gradual but substantial drop in malaria transmission (46-70%) occurred from 1994 to 2007, followed by a marginal increase beginning in 2008 or 2009. In particular, proportionate changes in seroprevalence and SCR point estimates (relative to 1994 baseline values) for AMA-1 and CSP, but not MSP-119, correlated closely with trends in parasite prevalence throughout the entire 15-year study period. However, retrospective analyses using datasets from 2007, 2008 and 2009 failed to detect any abrupt drop in transmission coinciding with the timing of the 1997-1999 ITN trial. CONCLUSIONS: In this highly endemic area, serological markers were useful for generating accurate point estimates of malaria transmission intensity, but not for retrospective analysis of historical changes. Further investigation, including exploration of different malaria antigens and/or alternative models of population seroconversion, may yield serological tools that are more informative in high transmission settings. |
Diarrhea in children less than two years of age with known HIV status in Kisumu, Kenya
van Eijk AM , Brooks JT , Adcock PM , Garrett V , Eberhard M , Rosen DH , Ayisi JG , Ochieng JB , Kumar L , Gentsch JR , Nahlen BL , Mintz ED , Slutsker L . Int J Infect Dis 2010 14 (3) e220-5 OBJECTIVE: To compare the frequency and etiology of diarrhea in children aged less than 2 years with known HIV status. METHODS: This was a nested cohort study, whereby children were followed during monthly routine and unscheduled visits. The HIV status of children was determined with PCR. A stool culture was obtained from children with diarrhea. A subset of stool samples was examined for parasites and tested for rotavirus. RESULTS: Between 1997 and 2001, 682 children (51.0% male) contributed observation periods with a mean of 47 weeks. Overall there were 198 episodes of diarrhea per 100 child-years of observation (CYO); diarrhea was more common among HIV-positive children than among HIV-negative children (321 vs. 183 episodes/100 CYO, respectively, p<0.01) and was not statistically different for HIV-negative children born to HIV-positive compared with HIV-negative mothers (182 vs. 187 episodes/100 CYO, respectively, p=0.36). For 66.5% of the acute episodes a stool culture was obtained; 27.8% of stool cultures yielded a bacterial pathogen. A positive stool culture was less likely among HIV-positive children compared to children of HIV-negative mothers (20.5% vs. 34.3%, p=0.01). Susceptibility of Salmonella and Shigella to commonly used antibiotics was low. Rotavirus was detected in 13.9% of 202 examined stool samples, and a stool parasite in 3.8% of 394 samples. Diarrhea was associated with 37.8% of child deaths. CONCLUSIONS: Diarrhea was more common among HIV-infected children, but was not associated with specific bacterial pathogens. Measures that reduce diarrhea will benefit all children, but may benefit HIV-infected children in particular. |
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