From all of the 10 health facilities investigated (), we were able to count individual laboratory records of 356,282 malaria slide examinations for the 7 year period from January 2003 to December 2009, with no more than one month missing data from any site except Bwiam Hospital (this facility opened in January 2004). Of these, 112,575 examinations had been conducted in four of the sites for the period 2003–2007 and analysed in our previous report 
, while 243,707 are unreported data from these sites over the past two years and from the other six sites over the whole period. Overall crude proportions of slides positive were reduced approximately 4-fold, from 32.8% (19,284/58,851) in 2003 to 8.5% (5145/60,669) in 2009, and the mean positivity across individual sites was reduced from 38.9% in 2003 to 7.2% in 2009.
Each of the six newly studied health facilities showed highly significant declines in the numbers and proportions of malaria positive slides (). Five of these had continuously significant annual declines over several years, from 2004 onwards (at Fajikunda and Bwiam) or 2005 onwards (at Serekunda, Soma, and Basse). At the remaining site (Bansang) there was a significant decline only after 2008. Comparing the last year (2009) with the first year in the data series (2004 for Bwiam, 2003 for other sites), proportions positive underwent reductions of approximately 14-fold in Soma (RR
0.07, 95% CI 0.06–0.08) and Bwiam (RR
0.07, 95% CI 0.06–0.09), approximately 5-fold in Basse (RR
0.18, 95% CI 0.16–0.20) and Serekunda (RR
0.19, 95% CI 0.18–0.20), approximately 3-fold in Fajikunda (RR
0.30, 95% CI 0.29–0.32) and 2-fold in Bansang (RR
0.46, 95% CI 0.42–0.50).
Malaria trends during 2003–2009 at 6 newly-surveyed health facilities in The Gambia.
All four sites for which data until 2007 had been previously reported 
and that had laboratory quality control throughout the period of data recording also showed significant declines in the numbers and proportions of positive slides (). Comparing 2009 with 2003, proportions positive underwent reductions of approximately 17-fold in Farafenni (RR
0.06, 95% CI 0.05–0.07), 8-fold in Keneba (RR
0.12, 95% CI 0.05–0.32), 5-fold in Fajara (RR
0.21, 95% CI 0.19–0.23), and 3-fold in Brikama (RR
0.29, 95% CI 0.27–0.31). The expected strong seasonality of malaria is highly evident at these sites, with few malaria positive slides during the dry season, contrasting with maximum numbers during and immediately following the annual rains. This seasonal pattern was also apparent at the other sites, although less marked due to a background of positive slides recorded during the dry seasons. Multiple regression analysis showed significant seasonality in numbers of positive slides at each of the ten sites, although this was stronger for those that had laboratory quality control throughout the period (, lower four sites). This analysis also confirmed year to year variation in numbers of slides positive. Fitting a linear model indicated average annual declines at each site of between 7.7% and 37.3%, although this simple model fitted poorly with data from some sites and other unknown causes accounted for between 4.6% and 40.4% of the overall year to year variation at each site ( and Figure S1
Malaria trends during 2003–2009 at 4 health facilities in The Gambia that had been previously surveyed until 2007.
Modelling of seasonality and average annual decline in numbers of malaria positive slides at each of the 10 health facilities studied in The Gambia
Two of the sites (Fajara and Brikama, both in the coastal Western Region) each showed continuous annual declines in malaria slide positivity down to <5% by 2006, after which proportions increased in the following two years before declining again, and we suspected that a few residual transmission foci (‘hotspots’) may have been responsible for this recent discontinuous trend. Therefore we analysed the geographical distribution of households of a sample of 285 confirmed malaria cases presenting to these facilities. This showed spatially broad distributions of these cases in each of the last three years, covering diverse urban and rural areas (), with no strong evidence of aggregation other than that expected from crudely known population density combined with proximity to the health facilities.
Spatial distribution of cases at two health facilities in the coastal area.
Community-based studies were performed to identify infection trends in two different rural populations. In the cohort of 800 children aged 1–15 years in 7 villages west of Farafenni under active and passive case detection from August 2008 to January 2009, a total of 223 febrile episodes were recorded, of which 24 (11%) were associated with malaria parasites. Such episodes occurred in 22 (2.8%) of the children in the cohort overall, with two children having two episodes each. There was no significant difference in risk of malaria with age, 13 episodes occurring among 361 children aged 5 years and under, and 11 episodes among 439 children aged 6 years and above.
In Brefet village, close to the River Gambia in the Western Region, sero-prevalence of anti-MSP-119
IgG antibodies was compared in plasma samples collected at the end of the transmission season (December) in 2006 and 2009. The proportion of MSP-119
sero-positives was lower in 2009 than 2006 in all age groups (). The most substantial difference between the years was apparent in children, with 19/97 (20%) of those 0–14 years of age being seropositive in 2006 compared to 2/53 (4%) in 2009 (p
0.008). The absence of detectable antibodies in any child sampled under 10 years of age in 2009 indicates that transmission of malaria in this community has been minimal for several years.