Introduction

Trachoma is the leading infectious cause of blindness world-wide, and a target for elimination by the World Health Organization [1]. The Alliance for the Global Elimination of Trachoma (GET) endorses the full SAFE strategy to eliminate trachoma; Surgery (for trichiasis), Antibiotics (to reduce the community pool of infection, Facial cleanliness (to decrease transmission), and Environmental improvement (to decrease transmission) [1]. Surveys to monitor the implementation of SAFE currently measure clinical signs of trachoma (trichiasis and Trachomatous inflammation—Follicular) and some measures of the household or community environment, such as larine coverage. There is no widely accepted measure of facial cleanliness.

Trachoma is spread through contact with infected ocular and nasal secretions as there is no intermediate host for the agent, C. trachomatis [1]. Therefore, researchers developed a standard observation of clean faces that reflect the presence or absence of these secretions on the face [2]. In the past, the presence of flies on the face was also included but was dropped due to transient nature of flies on the face and the impact of measurement conditions on ascertaining flies. Graders of clean faces have been shown to be reliable [2] and a clinical trial found evidence that improving clean faces resulted in decreasing prevalence of severe trachoma [3].

However, the observational metric has been criticized as not quantitative and thus insensitive to incremental changes in behavior [4]. There is also the concern that graders of clean faces may be influenced by the appearance of others in the household or the general conditions in the household or community. To this end, a new approach was developed using sterile individual saline facial wipes to measure the degree of dirt on the face against an eleven-step colorimetric chart [4].

The purpose of this study was to compare the measurement of both observed clean faces and observed degree of dirt as represented by the color of the facial wipe in a sample of 50 children ages 1-<7 from each of four communities in Kongwa Tanzania. Observations would be made prior to mothers washing the faces, immediately afterwards, and 4 hours afterwards. We hypothesized that both measures would be sensitive to face washing, but that both measures would return to pre-washed levels after 4 hours.

Methods

Preliminary study

A preliminary study was conducted measuring the effect of different colors of dirt, all common in Kongwa district and available at the study office, on the grading of wipes (see Fig 1). A standard 1/2 tsp of 3 different colors of available dirt, ground to the same consistency, was applied to the same area of the hand, which was washed and dried before and after each application. The wipe was applied as directed in protocol to the area, and then graded by SW without knowledge of the color of the dirt that was applied.

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Fig 1. Different colors of dirt in Kongwa Tanzania.

https://doi.org/10.1371/journal.pntd.0012090.g001

Study population

For the comparison study, we selected four communities and randomly selected 50–51 children from each community as described below. The communities were randomly assigned to either control (no face washing at any observation point) or one of the three intervention communities. The design and observation points are diagrammed in Fig 2.

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Fig 2. Diagram of study design and observation points for comparison study.

https://doi.org/10.1371/journal.pntd.0012090.g002

For study budget and logistic reasons, four communities in Kongwa district were chosen based on being within one hour drive from study headquarters (as noted below, the team had to revisit each house 4 hours after the second measurement and the day would be too long otherwise). The communities had to be reasonably close to one another to allow cars to drop off the census taker as part of the advance team in one community, and the survey team in another. Each community had a census of all households with children aged between one and seven years. Fifty households per community were randomly selected to participate. One child within the age range was randomly selected within the household. No household or child refused the study. Older children were not eligible for the study because they had to have their faces washed for school in the morning and would not be available for the observation later in the day. One community was randomly selected as a control, to monitor facial status over the course of the day in the absence of face washing. All children in the study were enrolled for one day in September/October 2022.

In November 2022, the children who had previously served as controls were revisited for one day. For this visit, we adhered to the intervention protocol and the mothers washed the children’s faces immediately after the baseline set of observations. The purpose of this visit was to ensure the control children were no different than the intervention children at least in response to face washing.

Results

The preliminary study found the grade for the wipe increased with the darkness of the dirt, range from grade 3 (darkest) to grade 8 (whitest) independent of the amount of dirt actually on the hand.

There were 91 children and seven graders who participated in the study of reliability of grading faces for cleanliness and face wipes for degree of darkness. Five graders observed 91 children twice. One grader observed and recorded 86 children the first time (she forgot to record 4 grades and one child was crying so not eligible)and 91 the second time (86 paired observations). One grader observed 90 children the first time and 90 children the second time (89 paired observations). The intragrader reliability for each grader was based on the number of children observed twice by each grader; the intergrader reliability for each pair of graders was based on the maximum number of children that had grades from both graders (21 kappa agreements total). The intragrader reliability for observing a clean face was kappa = 0.64, range of 0.47–0.78 (Table 1). The intergrader reliability was 0.53, kappa ranged from 0.36–0.75.

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Table 1. Intra and inter grader reliability of seven graders in observing the presence of a clean face, and grading a facial wipe in 91 children in Kongwa Tanzania.

https://doi.org/10.1371/journal.pntd.0012090.t001

All seven graders graded the color wipe twice, which was obtained on all 91 children. The intragrader reliability was weighted kappa = 0.57, range of 0.40–0.75. The intergrader reliability, excluding the one grader who was copying answers, was 0.52, with a score ranging from weighted kappa of 0.36–0.76. Overall, an estimated 79% of the 91 children had clean faces, with an average color wipe score of 8 (Table 1).

The comparison study of the two measures of a clean face, face wipe and observation of a clean face, was carried out in 202 children whose average age was 3 years (Table 2). Females were 55% of the control children and 59% of the children who were cleaned after the first observation.

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Table 2. Characteristics of the sample of children in the comparison of two measures of a clean face.

https://doi.org/10.1371/journal.pntd.0012090.t002

The pre cleaning values of all children were used to evaluate the correlation between the presence or absence of a clean face and the grade of the facial wipe. There was no association. Those with a clean face had a mean face wipe grade of 6.7 (SD = 0.68), while those with unclean face had a mean face wipe grade of 6.6 (SD = 0.78) (p = 0.75).

The children who were not washed over the study period did not have a significant difference in the proportion of clean faces observed at each time point (Table 3); at baseline 47% had clean faces, and 4 hours later 48% had clean faces. Among the children whose mothers washed their children after the pre-cleaning time point there was a significant improvement in observed clean faces immediately after washing, from 50%-88%. The clean faces persisted 4 hours later, with 65% having a clean face, compared to 48% in controls, a significant difference (p = .03)

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Table 3. Proportion of observed clean faces in children enrolled in the control and washed child study group at each time point.

https://doi.org/10.1371/journal.pntd.0012090.t003

Similar analyses were conducted comparing the data from the grading of the face wipe in children in the control community to the children in the others whose faces were cleaned after the first observation (Table 4). There was no difference in the two groups at baseline, but a significant difference in the means immediately after facial cleaning, with less dirt on the wipes from the cleaned children, mean 8.0, compared to the control children, mean 6.7. Although the cleanliness declined after four hours, a significant difference persisted, with a control mean of 6.7 versus a mean of 7.1 in the children who had been washed four hours earlier.

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Table 4. Mean and median of face wipe grade* in children in the control and washed child villages at each time point.

https://doi.org/10.1371/journal.pntd.0012090.t004

We sought further reassurance that the control children were similar to the children who were cleaned after the baseline observation. We observed the control children using the same 3 observation points again one month later, but this time having their mothers wash their faces after the baseline observation. (Table 5). Two of the children were not available one month later, so the paired comparison was conducted with 48 children. There was no difference in the distribution of children who were observed to have clean or unclean faces prior to washing at baseline compared to one month later, and in fact it was not the case that all the children observed to be clean were those clean again at the one month baseline visit (paired test p = 0.4) As expected, immediately after face washing the children all had clean faces observed compared to the observation of clean face when no washing was done. At the 2^nd follow-up visit the proportion with clean faces was 50% when they had not been washed previously and 65% when they had been washed previously; evidence of a decline after four hours but not to the level seen without washing. The difference was not statistically significant.

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Table 5. Paired comparison of 48 children who had no face washing at baseline (control) but had faces cleaned after initial observation one month later.

Clean Face observations.

https://doi.org/10.1371/journal.pntd.0012090.t005

The same comparison was made for the face wipe grade. We found that the two baseline observations (prior to washing) suggested the same children had a cleaner face wipe score one month later compared to their face wipe score previously. The mean difference in score was 0.29, p = 0.02 (Table 6). This significant difference could indicate a secular trend in cleanliness of children or a trend in higher scores in grading over time, although the period of time between assessments was just one month. As expected, there was a significant increase in the score graded for the face wipe after face washing compared to the score graded in the same children in the absence of face washing, an increase of 1.94 or almost 2 grades. The change in the face wipe grade also declined after four hours from face washing but was still statistically significantly higher than the grade in the same children without washing.

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Table 6. Paired comparison of 48 children who had no face washing at baseline (control) but had faces cleaned after initial observation one month later.

Observations on Face Wipes.

https://doi.org/10.1371/journal.pntd.0012090.t006

Discussion

The purpose of this study was to compare the performance of two measures of a clean face. One measures the observation of ocular and/or nasal discharge on the face, and the other measures the degree of dirt on the face. There was no correlation between the two measures. In part, this may be due to the variability in the color of dirt, as darker dirt would give a higher score than the same quantity of lighter colored dirt on the same face. In part it is also because the measures are not assessing the same metric. Ocular and nasal discharge may be present on an otherwise clean face if the eyes and nose were not specifically wiped, and wiping discharge with a dirty cloth may leave residual dirt on the face.

For both measures, the reliability among and between graders was similar. The agreement between graders in observing a clean face was lower than has been reported (2), and maybe due in part to mothers cleaning the child’s face midway in the exercise despite being asked not to do so. The exercise was carried out in a central location, and being around other mothers may have resulted in feeling peer pressure to clean the child. We found a higher proportion of children with clean faces (and a higher face wipe grade) during the reliability test than when we did the observations at the home, providing further support for the possible peer pressure effect of doing the reliability study at a central location. This finding was similar to an earlier finding comparing clean faces at a central site versus at the home [5] The relatively low kappa agreement, even weighted, in grading the face wipe was also lower than reported elsewhere (4). Comments from the trainer and trainees suggest the difficulty seemed to arise from determining the area around the darkest patch on the wipe, especially if there were multiple dark patches. This could arise if there was shifting pressure between fingers during the wiping process.

For the cross-sectional comparison, the group that later had faces cleaned was no different in either the proportion of clean faces or the grade on the face wipe compared to the control group at the first measurement time. This similarity provides reassurance of the comparability of the two groups, and that changes over time are likely to be real. Both measures of clean faces were sensitive to the face cleaning of children compared to control children, with significant differences in the proportion of clean faces and improvement in the face wipe score measured after cleaning. After four hours, some loss in cleanliness over time was expected in the group of children whose faces were washed, but they still were significantly different from the control children with a higher percentage of clean faces and higher face wipe score. We were concerned that the face wipe score might be artificially high at 4-hour observation because the same eye was wiped pre-cleaning and again at 4 hours. Rather than a reflection of the face washing, the cleanliness could be a reflection of the use of the facial wipe itself. However, the fact that in the group of control children who were not cleaned, the baseline and 4-hour observation of the facial wipe were similar (see Table 3) suggested the impact of using the wipe itself was minimal.

The findings on some loss of cleanliness but not to pre-washing levels were interesting because the children in the study were the youngest ones, and immediately after the team left the house, were observed to go back to playing in the dirt around the household. The mothers were specifically asked not to wash the child again until after we returned 4 hours later, but it is possible some mothers performed an interim face cleaning on the child. We felt this was a relatively rare event because there was no evidence the mothers of children in the control community cleaned the children during the four hours and they would have had as much incentive to do so as the mothers of children who were cleaned.

We repeated the observations on the children in the control community one month later, only this time asking the mothers to wash the children after the first observation. This paired comparison would enable us to see if the children in the control community did behave similarly to the children in the communities where faces were cleaned after the first observation. We found that the proportion of children with clean faces at the first observation, 52%, was statistically the same, 56%, as at one month later. However, the grade of the face wipe was significantly higher at one month in the same children compared to their value previously, a difference in the score of the two of 0.29. Because the facial cleanliness grader was different from the face wipe grader, and the two observations were masked from each other, we do not feel the improvement over time was a secular trend in grading. Rather, the improvement may be due to circumstances in the households or community. Since only one month separated the observations, it is unclear what those circumstances may have been. The team reported no noticeable changes in the environment had occurred in the community. It is possible that some mothers washed their child’s face prior to the baseline visit in the second round, despite being asked not to.

The finding of differences in the baseline measurements does mean that the measurements finding improved cleanliness comparing the first set of measurements to the second set one month later must take into account that there were unexpected differences at baseline in levels of cleanliness as well. Nevertheless, there was a significant improvement in the proportion of clean faces and in the face wipe grade immediately after cleaning, compared to the respective metrics in the same children with no cleaning. This is not surprising and expected. The magnitude of change was higher than expected, with 100% of children observed to have clean faces and a score on the face wipe that increased by almost two grades. In part some of this may reflect the secular trend in cleanliness observed at baseline, but not all. The observations made 4 hours later also showed that some effect of cleaning the child’s face persisted, with 56% of children still clean after washing compared to 50% in the same children in the absence of washing. The absence of statistical significance may reflect the sample size of 48 children; we would have needed 181 children to detect the difference observed. The face wipe grade was statistically significantly higher at 4 hours post cleaning compared to the face wipe grade in the same children at 4 hours without cleaning, with a difference of almost one grade. Because the results from our paired comparison of the control children were similar to the results in the study comparing the control children to the 151 children who had their faces washed after baseline, we feel that the children in the control community were not very different from those in the communities where face cleaning was carried out initially.

There were limitations to the study. Due to logistic considerations, we were not able to measure facial cleanliness longer than four hours after cleaning. It is possible that there would be differences in the two metrics if we had been able to study the aspect longer. Also, we observed some mothers cleaning the child’s face between round one and two of the reliability study, so the agreement within and between graders was not as high as it would have been if no cleaning had been done. We did not have field experience training the graders on grading the face wipes and felt we did not allocate adequate time for this, despite adding an afternoon and evening training to the original day allotted. We allowed the mothers to clean the child’s face as they usually would, and in some cases, it was clear the eyes or nose were not targeted, or that the child would not permit time to get all the dirt off. This may have affected the observation immediately after cleaning, and why the scale on the face grade was not fully used. We noted that although the scale for grading the face wipe went from 0–10, and was set up to be quantitative, in fact rarely were any scores outside of 6–8. We recognize that the for the control group, the face and wipe graders may have remembered the previous grade they assigned at baseline and thus the agreement between baseline and immediate first follow up was tighter than it might have been if two graders had carried out the grading.

In summary, both metrics for measuring a clean face had similar measures of reliability, and both detected change in facial cleanliness that resulted from cleaning a child’s face. Both showed an ability to detect the change immediately after cleaning and four hours later, even with a decline in facial cleanliness over the four hours. In our experience there were both positive and negative considerations with each method. In terms of training, it was hard for trainees to learn how to pick a spot on the wipe to grade, especially with multiple dark spots, and training took longer than for observing the presence or absence of a clean face. In terms of cost, the simple observation of a clean face and the observation of a facial wipe both require personnel training; however, there is the additional cost of the procurement of sterile saline wipes, transport to the field, and proper disposal of the wipe and the packet. The use of a binary variable, face clean or unclean, may not be sensitive to incremental change compared to a scale of eleven points. In reality though, the extreme values were never used and the scale ranged largely from 6–8 with an occasional 5 or 9. Nevertheless, differences of less than a grade were detected which suggests that a smaller sample size may be possible to detect change when using the facial wipe. However, such a small change has unclear meaning as our data suggest that face washing results in at least 1–2 unit change in face wipe grading to reflect the behavior, and a 17–30% difference in the percentage of clean faces. These are big changes. Our observations from the paired analyses suggest differences of less than a unit with the facial wipe, or less than 10% in observation of clean faces may reflect noise in grading rather than true, population based, behavior change.

As noted before, the metrics measure different aspects of a clean face. If dirt is the metric of interest, then observing a clean face as defined here will not reliably capture that aspect. Similarly, if ocular and nasal discharge is the metric of interest, then a facial wipe will not reliably capture the absence of those elements. Both measurements appear to capture the behavior of facial cleaning, and the choice would appear to rest on the measurement that captures the stated objective of the behavior, consideration of costs, training, logistics, and implementation.