Brief Report

Effect of Households’ Social Networks on Lice Infestation

among Vulnerable Mexican Children: a Qualitative

Comparative Analysis

by Lydia Ortega-Marın,1 Margarita Marquez-Serrano,2 Luz M. Lara-Lopez,3 Ligia I. Moncada,4 and Alvaro J. Idrovo5

1General Direction of Health Promotion, Sub-Ministry of Prevention & Promotion, Ministry of Health. Mexico City, Mexico2Centre for Health System Research, National Institute of Public Health. Cuernavaca, Morelos, Mexico3Academic Secretary, National Institute of Public Health. Cuernavaca, Morelos, Mexico4Public & Tropical Health Department, School of Medicine, National University of Colombia. Bogota, DC, Colombia5Cardiovascular Foundation of Colombia. Floridablanca, Santander, Colombia, and Public Health Department,

School of Medicine, Industrial University of Santander. Bucaramanga, Santander, Colombia

Correspondence: Margarita Marquez-Serrano. E-mail:<margarita.marquez@insp.mx>.

Correspondence address: Avenida Universidad 655. Colonia Santa Marıa Ahuacatitlan, CP. 62100. Cuernavaca, Morelos, Mexico.

Summary

The prevalence of pediculosis is high among elementary and secondary school children, which favors the

belief that infestation occurs more often in schools than in homes. This study explored the role of

households’ social networks in the transmission of head lice. Seventeen school children and their

social networks (n¼ 22) from Acatlipa (Morelos, Mexico) participated in a prospective observationalstudy during school vacation. The hair of all the school children was washed with shampoo containing

permethrin at the beginning of the study and the incidence of pediculosis (O) was evaluated at the

beginning of the school term (follow-up at 1.5 months). The sets included in the qualitative comparativeanalysis were sex (S), length of hair (H), baseline diagnostic of pediculosis (I) and degree (D) and

infestation index (N) obtained through the analysis of social networks. The prevalence of pediculosis

was the same at the beginning and the end of follow-up (17.6%). The degree of the school children’s

networks ranged between 2 and 14. There were 8 configurations, the most frequent being F*i*d*n*h.The most parsimonious configuration associated with the incidence of pediculosis was F*I*d*H (female,

previous infestation, low degree and long hair), with a coverage of 0.344 and a consistency of 0.941.

Indicators of social networks made it possible to identify the role of households’ social networks in the

transmission of lice. Individual actions such as the use of shampoo containing insecticides are temporaryand, therefore, structural actions should be favored.

Key words: lice infestation, school children, social network analysis, neglected diseases, poverty,

Mexico.

Introduction

Infestation of head lice is produced by Pediculushumanus var. capitis. Because this is not usually

included as a priority for health programs, there arefew efforts to control it, such that it is considered tobe a neglected parasitism [1]. Prevalence of infest-ation is heterogeneous among nations, populationsand cultures (0.7–61.4%). However, higher preva-lences are frequent among school children, girls andwomen [2]. In Mexico, there are only three studies onpediculosis, and prevalences were ranging between 18and 60% [3]. The belief that school is the primary siteof contagion has become widespread, minimizing therole that the household may play in transmission andfavoring the stigmatization of infested individuals.

Acknowledgements

We would like to thank the participants in the studyand teachers for their collaboration during the fieldwork. This study was supported by the MexicanNational Institute of Public Health.

JOURNAL OF TROPICAL PEDIATRICS, VOL. 59, NO. 5, 2013

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Infested children are frequently not permitted toattend school even though it is known that this meas-ure is not adequate for controlling pediculosis [4].Household is a propitious site of contagion becauseit is where the children interact closely with theirfamilies, facilitating transmission by head–head con-tact, which is known to be the primary means ofinfestation [5].

Lice infestation is recognized as a stigmatizingcondition because it is an undesirable attribute ofsociety’s members [6]. However, the stigmatizationis not restricted to children, and their relatives arestigmatized too. A good way to explain social phe-nomena related with lice infestation is ‘shared vulner-ability’ model [7]. This theoretical model uses fourstages (‘being ostracized, losing integrity of the self,struggling with persistence and managing strain’) toexplain why some individuals have persistent infest-ation. Because it specifically mentions that ‘losingintegrity of the self’ is expressed by social isolation,modification of family relationships and feelings ofguilt [7], the model can be useful as theoretical basisto understand the effect of households’ social net-works on lice infestation.

ContextA population health diagnostic was conducted be-tween 2010 and 2011 in the neighborhood of RıoEscondido in Acatlipa (Morelos, Mexico) as part ofan educational practicum with public health students[8]. During this diagnostics, pediculosis was identifiedto be a problem that mainly affected elementaryschool children. The adults responsible for address-ing it held beliefs that were not consistent with scien-tific knowledge, especially in terms of the means ofcontagion and available treatment. Thus, it wasdecided to conduct a study culturally adaptedto the community [9] that would serve to provideevidence of the adequate implementation of interven-tions to control infestation. In this context, theobjective of this study was to explore the role ofhouseholds’ social networks in the incidence ofpediculosis.

Methods

A prospective study was conducted in which17 school children and their social networks partici-pated during the summer break. The baseline servedas a diagnostic and ensured the treatment of infest-ation before follow-up. A questionnaire was admin-istered, which included sociodemographic data andcharacteristics of the hair. This study was approvedby the ethics commission of the Mexican NationalInstitute of Public Health.

The school children were visited in their homesduring the vacation period (July and August, 2011),after receiving authorization by their guardians.Their heads were inspected, and a detailed

explanation was provided to one of the parentsabout all the steps to be followed. The wet combingtechnique was used [10, 11], which was carried outwith a special comb and conditioner. The hair wasconsidered long if its length exceeded the shouldersand short if it was not >5 cm from the scalp. The hairwas divided into quadrants for washing, and wastaken one by one, dividing it into small locks thatwere combed with conditioner. As the locks werecleaned they were tied with bands. The comb wasthen cleaned with white paper.Following this, they were asked about close con-

tacts during vacation, and the heads of their contactswere also inspected when they agreed to it. One of theresearchers washed the hair of the child attendingschool and that of the members of his or her socialnetwork who had lice, with a commercial shampoocontaining 5 g/100ml permethrin. During this pro-cess, one of the parents was explained the correctdosage and application time for effective use. Theywere given the shampoo so as to conduct the washingthree times to prevent infestation. A second inspec-tion of the heads was conducted at school on the firstday of class to evaluate infestation.

Social network analysisA symmetrical matrix was plotted with the datafrom the social networks using the programNetDraw. [12] The density of the network was thencalculated as well as the degree for each node usingthe program UCINET. [13] Density is a measure-ment used to express the number of contacts betweennodes and is calculated as the ratio between contactpairs divided by the maximum number of possiblecontacts. [14] The degree is the number of directcontacts associated with each node [15], which forthis study can be interpreted as a greater probabilityof P. humanus var. capitis infestation. The transmis-sibility index was also calculated, based on the degreeand the infestation status of the nodes involved,as follows:

Transmissibility Index ¼

½# infested nodes�1þ ð#non-evaluated�0:5Þ�=

degree:

Note that a score of 0.5 was assigned to non-evaluated nodes owing to uncertainty, in accordancewith fuzzy logic [16].

Qualitative Comparative AnalysisThe use of a qualitative comparative analysis (QCA)was chosen because the size of the available samplewas small. This method and analytical theory enablescombining quantitative and qualitative approaches[17]. In recent years, it has begun to be used inpublic health studies [18, 19] to explore whether oneor several combinations of attributes (configurations)

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are associated with one outcome [19, 20]. In add-ition to exploring several causal routes, it is also pos-sible to include outliers, unlike conventionalstatistical methods [20]. The causal logic of theQCA is similar to classical epidemiological proposalsincluding concepts as necessary and sufficient causes[21–22].

During calibration, the original variables weretransformed to obtain values between 0 (total non-membership, indicated with a lower case letter) and 1(total membership, indicated with a capital letter).The dichotomous variables assumed a referencevalue in which female¼ 1 (F), long hair¼ 1 (H), pre-vious infestation¼ 1 (I) and new infestation¼ 1 (O).

TABLE 1Characteristics of children participating in the study. Acatlipa, Morelos, Mexico, 2011

Case Sex Hair Basal examination Degreea Infestation indexb Final examination

1 Male Short No 6 0.583 No2 Male Short No 14 0.429 No3 Female Medium No 9 0.444 No4 Male Short No 6 0.250 No5 Female Long No 6 0.250 No6 Male Short No 9 0.500 No7 Female Medium Yes 10 0.500 Yes8 Female Long No 2 0.750 No9 Male Short No 4 0.250 No10 Male Short No 9 0.500 No11 Male Short No 9 0.278 No12 Female Long Yes 7 0.571 No13 Female Long No 8 0.438 Yes14 Female Long Yes 8 0.688 Yes15 Male Short No 2 0.250 No16 Male Short No 8 0.500 No17 Female Long No 5 0.600 NoSet F H I D N O

In bold letters the attribute with score¼ 0.5aObtained during social network analysis.bBased on the number of infected nodes/degree (description in the text).

FIG. 1. Social networks of children during school holidays. Square: woman; circle: man; black: pediculosis;white: no pediculosis; gray: unknown.

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In terms of hair, there were some cases of mediumlength, which were assigned a score of 0.5. Degree(D) was transformed using the standardizationmethod and the infestation index (N) was constantbecause it was a ratio.

The possible configurations underwent two tests.The first evaluated consistency versus inconsistency,considered to be met when the consistency of theevaluated configuration (y) is greater than that ofthe complementary configuration (1–y). The se-cond test evaluated whether the consistency of eachconfiguration exceeded a fixed value of 0.75. Then,the configurations that met both tests were determinedand, finally, the most parsimonious configuration wasidentified. The analyses were conducted with the fuzzymacro [23] using the Stata 11 statistical program (StataCorporation, College Station, TX, USA).

Results

Some of the characteristics of the children participat-ing in the study are in Table 1. There were slightlymore males (9 of 17), 9/17 had short hair, 2/17 hadmedium length hair and 6/17 had long hair. Note thatthere were three cases with pediculosis before andafter the intervention (17.6%, 95% CI: 3.8–43.4),two of which presented infestation at both times.

The egocentric social networks during vacationincluded 122 nodes, with a density of 0.0145 and astandard deviation of 0.1206 (Fig. 1). The degree pre-sented values between 2 and 14 (median: 8). It waspossible to directly evaluate 40.98% (n¼ 50) of thetotal of nodes, observing 43 cases. Thus, the observedprevalence was 40.28%, which decreased to 35.25%when considering all the nodes in the network. Theinfestation index had values between 0.25 and 0.75(median: 0.5), indicating the potential presence ofpediculosis in all the social networks.

The truth table with the eight configurations pre-sent among children shows that those most fre-quently observed were F*i*d*n*h, F*i*D*n*h and

F*i*d*N*H (Table 2). The configurations thatmet both tests were F*I*d*n*H and F*I*d*N*H,which could be reduced to a single parsimonious con-figuration, F*I*d*H. This attained a total coverageof 0.344 and a consistency of 0.941.

Discussion

This study was able to identify a profile associatedwith the occurrence of pediculosis in the home, char-acterized by having had prior infestation, beingfemale, having long hair and a low number ofsocial network contacts. Among different popula-tions and cultures, studies have reported consistentlythat pediculosis is more frequent among those whohave already been infected [24, 25], who are female [2,26, 27] or have long hair [24–26]. This can be asso-ciated with females tending to play in the home withsmall groups with whom they have close contact,unlike males [28]. In similar contexts, high numberof women are in contact with children with lice in-festation (82.35%), and mothers are the most fre-quent infested relative (32.5%) [29]. Moreover, agreater occurrence has also been reported afterschool breaks [24–26].Nevertheless, to our knowledge, this is the first

study using social network analysis (SNA) to explorethe role of relationships between individuals in thetransmission of lice. This could only be demonstratedby including in the analysis the simplest centralityindicator because conventional analyses only takeinto account those who directly participate, withoutconsidering other individuals who may have an effect[30, 31]. The finding that infested children tend tohave fewer contacts in their social networks can beunderstood with the ‘shared vulnerability’ model [7].In this model, children with lice infestation and theirfamilies have social isolation; thus, effective interven-tions should include medical treatments and specificactions to facilitate the contact with wider socialnetworks and diminish stigmatization.This study also demonstrated that insecticides are

only partially effective and do not have a long-termeffect if structural determinants are not modified [25].Studies have shown that topical treatments usingneurotoxic insecticides have lost a considerabledegree of effectiveness [32–34]. Resistance to theseinsecticides can decrease their effectiveness [35, 36].Intervention with shampoo was conducted with allschool children and some members of their socialnetworks. It is therefore possible that the liceremained in individuals from networks without theintervention, there may not have been total adherenceto the intervention as indicated by the researchersor the parasites may even have been resistant tothe insecticides. These situations are common andstrengthen the idea that controlling lice requiresenduring actions involving social determinants. Thisstudy confirms that the use of insecticides is reallyeffective only if it is possible to assure that many

TABLE 2Truth table for configurations observed among children

participating in the studya

Configurations n %

F*I*D*N*H 1 8.33F*I*d*N*H 1 8.33F*i*D*n*H 1 8.33F*i*D*n*h 2 16.67F*i*d*N*H 2 16.67F*i*d*N*h 1 8.33F*i*d*n*H 1 8.33F*i*d*n*h 3 25.00

aFive cases were excluded because of an attribute havinga score¼ 0.5.

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school children and their networks of contacts aretreated at one time, as performed in developed coun-tries [37]. Unfortunately, these massive experiencesare expensive for developing countries, where thewealth is concentrated in small population groups.The results of the study should be interpreted con-

sidering some limitations. A small sample partici-pated in the study, making it impossible to observeeffects of the variables using conventional statisticaltests. Nevertheless, the analysis enabled exploringwhether there were one or more causal routes usinglogic based on an analysis of cases and not of theirvariables. This type of analysis turns out to be morecoherent, using theoretical approaches such as‘shared vulnerability’ [7]. A limitation associatedwith QCA is that it does not facilitate the explorationof many attributes. Therefore, from the perspectiveof conventional statistics, the study could be con-sidered confounding, while based on QCA logic itcan be considered adequate for observing the effectof social networks.In conclusion, this study provides evidence indicat-

ing the home as a context that facilitates the trans-mission of pediculosis when a series of attributes arecombined. SNA was a method to provide contribu-tions to the study of conditions in which there isdirect person-to-person infestation or individualsare grouped and relate according to certain sharedcharacteristics [31]. This knowledge, created withthe same community participating in a future inter-vention, enables generating reliable evidence that canbe used later by interventions that are more specificand culturally acceptable to the same population.

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