The prevalence of common skin conditions in Australian schoolstudents: 1. Common, plane and plantar viral warts

M.KILKENNY, K.MERLIN, R.YOUNG AND R.MARKSThe University of Melbourne, Department of Medicine (Dermatology), St Vincent’s Hospital, 41 Victoria Parade, Fitzroy 3065,Victoria, Australia

Accepted for publication 22 December 1997

Summary Although viral warts are common, their exact frequency in the community is often underestimatedand not well recorded. A random sample of 2491 students from schools throughout the State ofVictoria, Australia were examined by dermatologists and dermatology registrars to record theprevalence of common, plantar and plane warts. The overall prevalence of warts adjusted for the ageand sex of Victorian school children was 22% (95% confidence interval (CI) 20·1–20·7) varyingfrom 12% (95% CI 9·4–15·7) in 4–6 year olds to 24% (95% CI 18·3–30·4) in 16–18 year olds.Common warts were the most frequent (16%) compared with plantar warts (6%) and plane warts(2%). There was no difference in the overall frequency of warts between males and females and therewas no difference in frequency between those who had eczema and those who did not. Almost 40% ofthose found to have warts on examination had indicated on the survey questionnaire that they didnot have any of these lesions. Of those who knew that they had warts, only 38% had used anytreatment for them. These data, the first community-based prevalence data on warts ever publishedfrom Australia, confirm that warts are indeed common. They suggest the need for educationprogrammes in schools on the nature of these lesions and the treatment available.

Warts are common human papilloma virus (HPV)infections affecting most people at some stage in theirlifetime. More than 50 HPV types have been identified todate, with a tendency towards certain HPV subtypesassociated with particular clinical presentations of theselesions.1

The prevalence of warts in children has varied inpublished studies from 3 to 20%.2–4 In a cohort ofBritish school children, the prevalence increased from4% at the age of 11 years to 5% at the age of 16 years.5

In the studies reported to date, there has been consider-able disparity in the examiners recording the warts;they varied from school nurses, physical educationinstructors, medical officers to, on occasion, dermatol-ogists. Previous studies have been reported from Europe,the United States and New Zealand,2–6 but no popula-tion-based studies have ever been reported fromAustralia.

The present study aim was to determine theprevalence and number of warts in a stratified cross-section of school children throughout Victoria. Infor-mation was gathered on whether or not treatment hadbeen sought for the warts and from whom. The study

also documented the history and presence of acne,atopic dermatitis (eczema) and tinea. This is the firstof four reports on the prevalence of these conditions.

Patients and methods

Study population

The overall target population from whom the samplewas derived was all students enrolled in school yearlevels Prep (age 4–5 years) to year 12 (age 17–18 years)in Government, Catholic and Independent schools inthe State of Victoria in 1996/97. Enrolment statisticscollected by the Victorian State Education Departmentestimated that the total population was 767,765students.

A two-stage sampling process was undertaken. At thefirst stage, 20 primary schools and 20 secondaryschools were selected with a probability proportionalto the size of the target population. Schools with enrol-ments of less than 100 students were excluded. Initially,20 secondary schools were selected randomly by post-code and then one primary school was randomlyselected from the same postcode. Hence in one location

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Correspondence: Professor Robin Marks.

there was one primary and one secondary schoolselected. For each school selected, a replacementschool from the same stratum on the sampling framewas selected to ensure that a replacement school, ifnecessary, was in the vicinity of the school originallyselected.

In the second stage of sampling, one class wasrandomly selected within each year level of the school.From each class list, 15 students were then randomlyselected for inclusion in the survey. This was to enableus to examine in a reasonable time period sufficientnumbers from each class level in each school to fit inwith a randomized distribution of schools across theState of Victoria. Thus in secondary schools, 90 studentswere selected from the six levels and 105 students wereselected from the seven levels present in primary schools.

Recruitment of schools

A detailed procedure for recruitment of schools wasundertaken to ensure maximum participation. Insummary, this included initially a letter to each schoolPrincipal seeking approval for the survey. It provideddocumentation including a background explanation ofthe study, approval granted from the Ministry ofEducation, as well as documentation of approval fromthe relevant clinical Ethics Review Committees.

One week later the school Principal was contacted toorganize a meeting to explain the study further beforepermission was sought. Then following a meetingbetween the school Principal, project manager and theproject co-ordinator, agreement to participate wasgranted. The co-ordinator then sent survey kits foreach student selected containing a parent introductoryletter, an information brochure, a questionnaire and aconsent form. The questionnaire included demo-graphics of country of birth, date of birth, sex andpostcode, as well as the student’s personal history ofskin conditions, the treatment required and any familyhistory of atopy. Questionnaires were completed by theparents, or, in the secondary schools, by the students.They were requested to fill out the questionnaire, andindicate whether or not they agreed to be examinedduring the survey.

At the same time, a letter about the survey and acollection of survey kits was sent to the class teachers.This included information about the study, as well as aneducation resource kit on common skin diseases beingdetected in the survey. Schools were encouraged to usethe resources in health education classes as a way ofensuring maximum participation.

Data collection

On examination day, the schools were visited by anexamination team comprising a consultant dermatolo-gist, dermatology registrar, nurse, project manager andproject co-ordinator. The students were examined in aprivate room by a dermatologist and/or a dermatologyregistrar, with the nurse present. The examinationincluded the head and neck, upper and lower limbs,hands and feet. The sites were assessed in the samesequence for all students. The site, number and type ofwarts, if present, were recorded on the data collectionsheet.

Diagnostic definition

The clinical diagnosis was used for recording thefrequency of warts, as was the case for all previouspublished studies. The lesions were classified intocommon, plantar and plane warts according tostandard texts.1 A diagnostic criterion study was under-taken prior to the survey to develop and assess aminimum set of diagnostic criteria for common warts.These included site, colour, hyperkeratotic surface anddiscrete margin.7 The diagnosis according to thesecriteria was then compared with the clinical diagnosisof common warts made by clinicians trained in derma-tology. Diagnosis according to our minimum set ofdiagnostic criteria showed a specificity and sensitivityequal to or greater than when using the standardclinical diagnostic criteria.

Plane warts were flesh-coloured or slightly pigmenteddiscrete lesions slightly elevated on hands and face.Plantar warts were discrete flesh-coloured lesionswhich separated skin lines on the sole of the foot andmay have had the presence of small haemorrhageswithin them.

To assess interobserver variation, every 17th student(6% of the total study sample) was selected for exam-ination by two different clinicians. The results wereassessed for interobserver agreement on diagnosis ofwarts and for the number of lesions.

Data analysis

Data collected from students were coded, entered andverified on a relational database (FileMaker Pro Version4·0).8 The Statistical Package for Social Sciences (SPSSVersion 6·1) was used for analysis taking into accountthe stratified sampling technique.9 Prevalence estimateswere based on data weighted according to the age and

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sex of all children enrolled in schools in the State ofVictoria. Thus any deliberate or accidental over- orundersampling of each of the categories was adjustedon a proportional basis. Results were expressed in termsof prevalence rates with 95% exact confidence intervals.

Inter-observer agreement was assessed using theKappa statistic for categorical variables to comparepairs of examiners.

Results

Population sample

Of the 40 schools originally selected for the survey, sixdeclined to participate. They were replaced by sixequivalent schools, consisting of one primary schooland five secondary schools.

There were 3871 students selected for inclusion inthe survey of whom 2727 (70%) completed the ques-tionnaire and gave consent to be examined. Threehundred and six declined to be part of the survey but

179 of these filled out the questionnaire. Eight hundredand thirty-eight did not return the consent form. Of the2727 who gave consent, 2491 (91·3%) were examined.The remaining 236 students were away on the day thatthe examination team visited the school. The 2491students consisted of 1174 males and 1317 femaleswith the details of breakdown by age and sex given inTable 1. Most students (92%) were born in Australia,with 4% being born in Asia and the remainder from avariety of other countries.

With increasing age, there was an increasing reluc-tance to participate, particularly among the adoles-cents. There was no systematic difference in theprevalence of warts among schools with high and lowresponse rates in these older age groups.

Comparison of gender, type of school and age of thestudents who were not examined (including those whogave consent, but were away on the examination day)with those who were examined, revealed no statisticaldifference between the two groups. Similarly, compar-ison of completed questionnaire data (including thefrequency of self-report of warts) for those studentswho were not examined with those who were, revealedno differences between the two groups.

Inter-observer variation

Table 2 gives details of the interobserver agreement fordiagnosis and number of warts. They showed that ingeneral, particularly for common warts, the interobser-ver agreement was very good.

Prevalence of warts

Overall, the age- and sex-adjusted prevalence of wartswas 22% (95% CI, 20·1%–24·7%). Table 3 gives detailsof the prevalence of all warts by sex and age showing agenerally increasing prevalence with increasing age, upuntil adolescence when the prevalence tended to leveloff. There was no difference in the age-adjusted pre-valence between males and females, nor was there any

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Age ( years) 4–6 7–9 10–12 13–15 16–18

Total sample selected (n ¼ 3871) 507 912 918 888 646Consent given 81% 78% 78% 66% 49%Students examined 76% 73% 69% 61% 41%Male (n ¼ 1174) 179 318 306 254 117Female (n ¼ 1317) 206 347 330 285 149Total sample examined (n ¼ 2491) 385 665 636 539 266

Table 1. Breakdown of students examined byage and sex

Table 2. Inter-observer agreement for diagnosis and assessment ofnumber of warts

Positive agreementa (%) Kappa statistic (k)

Diagnosis

All warts 96·5 0·91Common warts 93·7 0·82Plantar warts 96·5 0·65Plane warts 94·4 0·17

Number of lesions (categorized into 1–2, 3–5, 6þ)

Common warts 82·1 0·62Plantar warts 80·0 0·55

aPositive agreement means the proportion of all positive responsesbetween paired investigators where both observers were in perfectagreement.

difference between the sexes when the lesions werebroken down into common, plantar and plane warts.

Of the 2491 students examined, 16% had commonwarts, 6% had plantar warts and 2% had plane warts.Only 333 (62%) of the 538 students who were found onclinical examination to have warts had reported ontheir questionnaire that they had warts. Two studentsdid not respond to this question. Thus: the sensitivitywas 62% (333 of 536) for knowledge of warts; thespecificity was 94% (2025 students said they did nothave warts and 203 did have them on examination);and the positive predictive value was 73% (456 students

said they had warts and only 333 of these had them onexamination).

There was a clear age-specific increase in commonwarts among males (Table 4). For the other warts, it canbe seen that there were several peaks in prevalence,particularly about the age of 10–12 years. In general,however, warts were less common among the primaryschool students (4–12 years) than among the second-ary school students (13–18 years).

With the exception of plane warts, most students hadone to two warts only (Table 5). With plane warts, overhalf of the students had three or more lesions. The vastmajority of common warts occurred on the upper limb,including the hands. Plane warts occurred on the legsmore often than common warts.

There was no difference in the prevalence of plantarand plane warts when comparing students from urbanand rural schools. However, the prevalence of commonwarts was higher in students from rural schools than inthose from urban schools (rural 19%, urban 14%, oddsratio 0·68, (95% CI), 0·54–0·85).

Association with eczema (dermatitis)

Comparison of the frequency of warts (28%) in thosestudents found to have eczema (dermatitis) with thefrequency (27%) in those without eczema revealed nodifference between the two groups. This applied not only

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Table 3. Prevalence overall of warts by age and sex

Prevalence (%) (95% CI)

Both sexes 22·4 (20·1–24·7)

Male 22·1 (19·5–24·8)Female 22·6 (19·4–25·8)

Age (years)

4–6 12·5 (9·4–15·7)7–9 21·6 (18·9–24·3)10–12 24·9 (20·0–29·9)13–15 23·5 (18·6–28·3)16–18 24·4 (18·3–30·4)

Table 4. Age- and sex-specific prevalence of warts by type of wart

Age ( years) Common warts Plantar warts Plane warts

Prevalence (95% CI) Prevalence (95% CI) Prevalence (95% CI)

Males

4–6 8·1 (2·9–13·3) 5·9 (2·8–8·9) 0·3 (0–0·9)a

7–9 14·8 (11·6–17·9) 7·9 (4·9–10·9) 1·8 (0·1–3·4)10–12 17·6 (12·7–22·4) 3·7 (2·2–5·2) 3·0 (0·9–5·2)13–15 21·2 (15·6–26·9) 6·8 (3·6–10·0) 1·6 (0–3·8)a

16–18 21·9 (13·1–30·7) 3·9 (0·7–7·1) 1·1 (0–2·4)a

Females

4–6 7·5 (3·9–11·0) 4·4 (1·7–7·1) 0·8 (0–2·0)a

7–9 15·4 (11·4–19·4) 5·9 (3·5–8·3) 1·4 (0·2–2·6)10–12 18·2 (13·3–23·1) 8·0 (4·2–11·9) 2·9 (1·2–4·5)13–15 16·8 (11·2–22·5) 5·7 (3·0–8·3) 1·5 (0–4·0)a

16–18 13·5 (7·0–20·1) 8·6 (4·3–12·9) 5·3 (1·9–8·7)

aIn these groups, where the number of cases was low, the lower confidence interval (CI) falls below zero as a statistical artefact of the formula used tocalculate the intervals. In these cases the lower limit has been recorded as zero.

for all warts, but also when broken down by type ofwart. Comparison of the frequency of warts amongthose students whose parents had reported that theyhad had eczema (dermatitis) at some time in the pastalso revealed no difference between those who had apast history of eczema and those who did not.

Treatment for warts

Of the 333 students found to have warts on examina-tion, and who had reported that they had them on thequestionnaire, 127 (38%) had used one or more pro-ducts to treat their condition. The people from whomthey sought treatment advice included medical practi-tioners (general practitioners, dermatologists, otherspecialists) (55%), pharmacists (31%), family/friends(9%) and others including beauticians and naturopaths(5%).

A total of 144 products, including liquid nitrogentherapy by a medical practitioner, were reported ashaving been used to treat the warts. Most of theseproducts were obtained as over-the-counter productsfrom the pharmacy (63%) without the need for aprescription. When coded as efficacious or not accord-ing to product type, 100% of those recommended by amedical practitioner or a pharmacist were coded aslikely to have some effect. On the other hand, 25% ofthose recommended by a family, friends or others werecoded as likely to have no effect whatsoever.

Discussion

The present study showed that warts are common witha prevalence of 24% overall, varying from 12% of 4–6 year olds to 24% of 16–18 year olds. Comparison ofthese data with those published previously reveals that

our prevalence is generally higher, not only in thenumber of warts overall, but in each of the individualcategories of common and plantar warts. To date therehas not been a study of sufficient size to record thefrequency of plane warts for comparison.

In our analysis of interobserver variation, althoughthe positive agreement was high for plane warts, theKappa statistic was low. This can occur as a result ofsmall numbers of respondents with plane warts asmuch as lack of agreement among observers.

A report of 13,423 children aged 3–18 years fromEast Anglia who were examined by school medicalofficers revealed a prevalence of plantar warts of 6%,almost identical to our study.10 However, their figure of9% prevalence for other warts falls far short of ours. Inour study, the observers were dermatologists and der-matology registrars, all medical practitioners who hadexperience and training in diagnosis of skin disease.This is in contrast to many previous studies where avariety of observers have been used with considerabledisparity in their training for recognition of commonskin diseases. This may be part of the explanation forhigher prevalence recorded in our study. In a previousreport where a single dermatologist examined 8298students in Sweden aged 12–17 years an overall pre-valence of warts of 20% was recorded in this agegroup.4 This study included common and plantarwarts but did not include plane warts.

There has been variation in the reports of frequencyby gender. The majority, like ours have reported nodifference, but in the East Anglia school children’ssurvey, 8% of females had plantar warts comparedwith 5% of males.9,10 A very large population-basedstudy in the United States reported that common wartswere more frequent in females than males.11

There has also been some variation in the reportedassociations between the prevalence of warts andeczema. The most recent report has suggested a reducedfrequency of warts in people with visible eczema afteradjustment for potential confounders.12 In our study,there was no difference in frequency between the twogroups. We used diagnostic criteria developed by theU.K. Working Party on Diagnostic Criteria for AtopicEczema to decide whether or not the students had atopiceczema.13 When we included the parental report ofprevious eczema that was not present in the examina-tion data, it did not alter our findings of the lack of arelationship of prevalence of warts to the presence ofeczema.

Almost 40% of students who were found to havewarts on the day of examination reported on the

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Table 5. Numbers per student and site of warts

Number 1–2 3–5 6þ

Common warts 72·6% 19·8% 7·6%Plantar warts 80·6% 11·6% 7·8%Plane warts 38·9% 18·5% 42·6%

Location Upper limb Lower limb Other

Common warts 84·2% 8·8% 7·0%Plane warts 71·2% 21·2% 7·7%

questionnaire that they did not have these lesions. Theaverage time between examination and the completionof the questionnaire was 4 weeks (range 2–8 weeks) soit is unlikely that a large number would have developedwarts or had them resolve in that interval. There was aspecific section on the questionnaire asking whether ornot they had warts, thus there was a prompt to remindthem. Some of this may have been forgetfulness, but onthe examination day, many of the children were notaware of any abnormality when they had the wartbrought to their attention. It could have been due todifficulty in recognizing lesions in the case of planewarts. In this group there was a slightly higher butnot statistically significant proportion of students notreporting them than for the other types of warts. Thisdoes not explain why they were not aware of commonor plantar warts.

Along similar lines, over 60% who knew that theyhad warts had not used any treatment for them. Thiscould have been a combination of factors including notbeing concerned about them, not believing they hadaccess to advice about treatment or not wanting treat-ment. We are unable to determine from our data whichof these, or other possible reasons, were the explanationfor lack of treatment being sought. It could be the basisfor a further study.

Finally, in those who had sought treatment, most hadgone to someone who was likely to have been in aposition to give reasonable advice, i.e. a medical practi-tioner or a pharmacist. Where a topical product wasused, the vast majority was bought over-the-counterfrom the pharmacy. Fortunately, all of the managementfrom these two sources was found to be potentiallyefficacious. On the other hand, although the numberswere smaller, 25% of the products recommended byeither friends or others were not likely to have anytherapeutic effect at all. There is a need for furthereducation about sources of advice for warts where theinformation received is likely to be of value.

In summary, this study has shown that warts arecommon in Australian school children. The prevalencewas found to be higher than in most studies reportedpreviously but the survey instrument of dermatologistsand dermatology trainees comprised a group of skilledobservers. With about one in four adolescents beingaffected by these lesions, there is a role for educationprogrammes within schools to highlight the potentialfor treatment, when desired. There is also a role foreducation about limiting the spread and prevention ofcross-infection, where possible, in the future.

Acknowledgments

The authors would like to acknowledge Dr JosephineYeatman, Mr Damien Jolley and Dr Malcolm Rosier whohelped in the design of the study. We would also like tothank Ms Val Bennett, the project nurse and Drs TanjaBohl, Barbara Breadon, Carol Burford, Annette Callen,Anthony Hall, Anne Howard, Michael Lee, Adrian Mar,Rod Sinclair and Craig Smith who comprised the der-matologists and dermatology registrars. Ms Anne Plun-kett assisted on the examination days and indevelopment and compilation of the report. This workwas supported by grants from the Australasian Collegeof Dermatologists; the Skin & Cancer Foundation, theJack Brockhoff Foundation (Victoria) and the WilliamAngliss Trust (Victoria).

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