Figure 4. Forest plot of the worldwide prevalence of free-living amoebae in swimming pools and recreational waters.
The global prevalence of FLA in swimming pools and recreational waters considering studies published up to 2010 (1977-2010) was considerably higher 51.54% (95% CI = 36.65 – 66.29) than in studies published after 2010 (>2010-2021) 37.95% (95% CI = 30.34 – 45.86). Considering the continents covered by the selected studies, the highest prevalence 59.52% (95% CI = 31.12 – 84.81) was reported in America and the lowest 34.65% (95% CI = 26.08 – 43.75) in Asia. Among the countries from which more than one study was included, Malaysia had the highest prevalence of FLA in swimming pools and recreational waters 89.33% (95% CI = 70.71 – 99.12), and the lowest prevalence 27.91% (95% CI = 18.73 – 38.13) was recorded in Taiwan. Considering the different sampling sources, the highest prevalence of FLA 52.27% (95% CI = 14.55– 88.50) was obtained in indoor heated pools, and the lowest prevalence 34.75% (95% CI = 20.85– 50.14) was obtained in other recreational waters. The analysis of studies that used only morphological methods to identify free-living amoebae showed the highest prevalence 56.41% (95% CI = 30.09 – 80.92), the lowest prevalence 22.32% (95% CI = 12.28 – 34.33) was obtained from studies based only on molecular methods (PCR), an intermediate prevalence value 39.94% (95% CI = 33.64 – 46.41) was obtained by analyzing studies that simultaneously used morphological and molecular methods (Table 2).
The subgroup analysis revealed that there were statistically significant differences between the overall prevalence of FLA in water sources and year (X 2 = 223.0, P < 0.001), continent (X 2= 71.9, P = 0.002), country (X 2= 46.4, P < 0.001), sample source (X 2 = 21.8, P = 0.003) and diagnostic method (X 2 = 274.0, P < 0.001) (Table 2).
Table 2. Subgroup analysis of FLA in water sources