Trichuris trichiura and the growth of primary schoolchildren in Panama

A survey of intestinal parasites including associated risk factors in humans in Panama

BACKGROUND

Intestinal parasitic infections are among the most common infections worldwide, leading to illness with serious and long lasting implications in children and immunocompromised people. Transmission of intestinal parasites is more frequent in tropical and sub-tropical areas where sanitation is poor and socioeconomic conditions are deficient. Panama is a country where climate and social conditions could be reflected in a high number of people infected with intestinal parasites. The presence, prevalence, and distribution of intestinal parasites in this country have been approached to date only in very restricted areas and population groups, but the impact of intestinal parasite infections at the national level is unknown.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted a cross-sectional survey between 2008 and 2010 to determine the prevalence of intestinal parasites across Panama. Overall, 14 municipalities in seven provinces of Panama were surveyed. The presence of eggs, cysts, and larvae was assessed by microscopy in 1123 human fecal samples using a concentration technique. A questionnaire to identify risk factors associated with the frequency of intestinal parasites in the study population was also prepared and performed. Overall, 47.4% of human samples presented parasites. Variables including community type, age group, occupation, co-presence of commensals and socioeconomic factors (use of shoes and type of sanitation) were significantly associated with intestinal parasites (p<0.05).

CONCLUSIONS/SIGNIFICANCE

The preliminary data obtained in the current study, showing a high prevalence of fecal-oral transmitted parasites in Panama, place intestinal parasitism as a major health problem in this country. Specific interventions should be planned for the indigenous population, the group most afflicted by intestinal parasites.

Using the prevalence of individual species of intestinal nematode worms to estimate the combined prevalence of any species

Objectives

To assess if a probabilistic model could be used to estimate the combined prevalence of infection with any species of intestinal nematode worm when only the separate prevalence of each species is reported, and to estimate the extent to which simply taking the highest individual species prevalence underestimates the combined prevalence.

Methods

Data were extracted from community surveys that reported both the proportion infected with individual species and the combined proportion infected, for a minimum sample of 100 individuals. The predicted combined proportion infected was calculated based on the assumption that the probability of infection with one species was independent of infection with another species, so the probability of combined infections was multiplicative.

Findings

Thirty-three reports describing 63 data sets from surveys conducted in 20 countries were identified. A strong correlation was found between the observed and predicted combined proportion infected (r = 0.996, P<0.001). When the observed and predicted values were plotted against each other, a small correction of the predicted combined prevalence by dividing by a factor of 1.06 achieved a near perfect correlation between the two sets of values. The difference between the single highest species prevalence and the observed combined prevalence was on average 7% or smaller at a prevalence of ≤40%, but at prevalences of 40–80%, the difference was about 12%.

Conclusions

A simple probabilistic model of combined infection with a small correction factor is proposed as a novel method to estimate the number of individuals that would benefit from mass deworming when data are reported only for separate species.

Mixed infections with roundworm, whipworm and hookworm are common, but survey reports often give only the separate prevalence of each type. However, the combined prevalence is important to estimate accurately the number of individuals who would benefit from control programmes and to make decisions about the frequency of treatment. Previous work suggests that mixed infections involving hookworm occur randomly, but that roundworm and whipworm infections are found together more frequently than would be expected by chance. We used 63 data sets from community surveys that reported both the proportions infected with individual types of worms and the combined proportion infected with any worm. We then calculated the proportion that would be infected with any type of worm if infections had occurred randomly and compared it with the observed combined proportion infected. We found a strong correlation between the observed and predicted combined proportions infected. A small downward correction of the predicted proportion infected by dividing by a factor of 1.06 brought it to a value that nearly equalled the observed proportion infected almost all the time. This simple model could be applied to published survey data to estimate accurately the number of individuals that would benefit from mass deworming.