Table 1.
Classes of soil-transmitted helminth infection intensities based on Kato-Katz fecal egg counts.
The fecal egg counts are expressed in eggs per gram of stool. The thresholds were introduced by the World Health Organization in 1987 and 1998 [5,6].
Table 2.
The intensity of soil-transmitted helminth infections measured by four microscopic methods.
The intensity of infections is summarized by arithmetic means of fecal egg counts (FECs; expressed as eggs per gram of stool (EPG)) and the proportion of light and moderate-to-high (M&H) intensity infections. For the classification of the infection intensity, we applied World Health Organization (WHO) infection intensity thresholds (see Table 1).
Table 3.
The probabilities to correctly classifying infections intensities based on WHO thresholds.
The World Health Organization (WHO) thresholds for classifying the intensity of infections into light, moderate and heavy are summarized in Table 1. The Kappa statistic reflects represents the degree of agreement in classifying M&HI infections between the microscopic methods (Mini-FLOTAC, FECPAKG2 and McMaster) and the reference method (Kato-Katz and WHO thresholds). 95% CI: 95% confidence interval; M&H: moderate-to-heavy.
Table 4.
Method-specific thresholds and the corresponding probabilities of classifying moderate-to-heavy and light intensity infections.
The method-specific thresholds were derived from receiver operating (ROC) curves for Mini-FLOTAC, FECPAKG2, McMaster and qPCR, separately. In these ROC analyses, the reference classification of moderate-to-heavy intensity (M&HI) infections was based on the Kato-Katz and the World Health Organization infection intensity thresholds (Table 1). They maximize the percentage of correctly classified M&HI infections while minimizing the percentage of light intensity infections falsely classified as M&H. The thresholds are expressed as eggs per gram of stool (EPG) for Mini-FLOTAC, FECPAKG2 and McMaster, and as the number of genome equivalents per ml of DNA (GE/ml) for qPCR. The Kappa reflects the degree of agreement in classifying M&HI infections based on the method-specific thresholds between the microscopic methods (Mini-FLOTAC, FECPAKG2 and McMaster) and the reference method (Kato-Katz and WHO thresholds). 95% CI: 95% confidence interval; M&H: moderate-to-heavy.
Fig 1.
Agreement in classifying infection intensities for Mini-FLOTAC when applying WHO and method-specific thresholds.
The scatter plots represent the degree of agreement between Mini-FLOTAC and a single Kato-Katz (1x KK; reference method) in classifying infection intensity based on World Health Organization (WHO; Table 1) or the method-specific thresholds (Table 4) for Ascaris, Trichuris and hookworms. The full black dots indicate that intensity of infection was correctly classified as light (bottom left quadrant) and moderate-to-heavy (M&H; top right quadrant). The red dots indicate that intensity of infection was falsely classified as light (bottom right quadrant) and M&H (top left quadrant). The full lines represent the thresholds, the dashed lined represents the line of equality.
Fig 2.
Agreement in classifying infection intensities for FECPAKG2 when applying WHO and method-specific thresholds.
The scatter plots represent the degree of agreement between FECPAKG2 and a single Kato-Katz (1x KK; reference method) in classifying infection intensity based on World Health Organization (WHO; Table 1) or the method-specific thresholds (Table 4) for Ascaris, Trichuris and hookworms. The full black dots indicate that intensity of infection was correctly classified as light (bottom left quadrant) and moderate-to-heavy (M&H; top right quadrant). The red dots indicate that intensity of infection was falsely classified as light (bottom right quadrant) and M&H (top left quadrant). The full lines represent the thresholds, the dashed line represents the line of equality.
Fig 3.
Agreement in classifying infection intensities for McMaster when applying WHO and method-specific thresholds.
The scatter plots represent the degree of agreement between McMaster and a single Kato-Katz (1x KK; reference method) in classifying infection intensity based on either World Health Organization (WHO; Table 1) and method-specific thresholds (Table 4) for Ascaris, Trichuris and hookworms. The full black dots indicate that intensity of infection was correctly classified as light (bottom left quadrant) and moderate-to-heavy (M&H; top right quadrant). The red dots indicate that intensity of infection was falsely classified as light (bottom right quadrant) and M&H (top left quadrant). The full lines represent the thresholds, the dashed line represents the line of equality.
Fig 4.
Agreement in classifying infection intensities between Kato-Katz and qPCR.
The scatter plots represent the de degree agreement between qPCR and a single Kato-Katz (1x KK; reference method) in classifying infection intensity cases based World Health Organization (WHO; Table 1) and method-specific thresholds (Table 4) for Ascaris, Trichuris and hookworms. The full black dots indicate that intensity of infection was correctly classified as light (bottom left quadrant) and moderate-to-heavy (M&H; top right quadrant). The red dots indicate that intensity of infection was falsely classified as light (bottom right quadrant) and M&H (top left quadrant). The full lines represent the thresholds, the dashed line represents the line of equality.