Secondary Logo

Journal Logo


Phthirus pubis in a Sexually Transmitted Diseases Unit

A Study of 14 Years


Author Information
Sexually Transmitted Diseases: April 2003 - Volume 30 - Issue 4 - p 292-296
  • Free

THERE HAVE BEEN FEW epidemiologic studies of pubic lice, and the exact incidence is unknown, but it is a common disease among sexually active young adults. 1,2 Infestations with pubic lice are more common in people of low socioeconomic status 3 and are frequently associated with the presence of other sexually transmitted infections. 4 It has been stated than the population with the highest incidence of pubic lice is similar to that with a high incidence of gonorrhea and syphilis: single persons and those between 15 and 25 years of age. 5

The objective of the current study was to show the clinical experience in Spain and to reevaluate the trends in prevalence as well as the epidemiologic patterns in a large series of patients in our sexually transmitted disease (STD) unit during the 14-year period of 1988 to 2001.

Patients and Methods

The study included 9093 patients (5693 female prostitutes and 3400 males, of whom 152 were men who had sex with men [MSM]) who attended the STD unit in Gijón (Asturias, Spain) between 1988 and 2001. The diagnosis of crab lice was made by visual inspection, with magnifying glass, for lice or nits on all patients who attended the STD unit. Pediculicide treatment was reevaluated after completion of a 7-day course of treatment for all patients and their partners. We included as a control group the 8896 patients without lice who attended the clinic during the period of study.

Other STDs were diagnosed according to the same protocol for all patients.

  • (1) A smear of the urethral exudate or, if no exudate was present, an endourethral sample taken with an alginate swab inserted 3 to 4 cm into the urethra or cervix was gram-stained. The finding of more than 5 polymorphonuclear leukocytes (PMNs) per high-power field (×100) in a gram-stained urethral smear from a man and of 10 PMNs in a smear from a woman was considered evidence of urethritis.
  • (2) Two alginate swabs of urethral/cervical or vaginal exudates were used to inoculate each of the following media (all from bioMeriéux, Marcy-l′Etoile, France): chocolate agar with 1% Isovitalex and VCAT (vancomycin, colimycin, amphotericin B, and trimethoprim) for Neisseria gonorrhoeae; HBT (human blood bilayer Tween) agar for Gardnerella vaginalis; Sabouraud agar for yeast; and chocolate agar with 1% Isovitalex and blood agar for other pathogens. Diamond medium (Oxoid, Basingstoke, UK) cultured directly in the STD unit was used for detection of Trichomonas vaginalis.Streptococcus agalactiae, Haemophilus species, Gardnerella vaginalis, and other bacteria were identified according to previously published methods. 6
  • (3) Urethral samples from men for culture of Mycoplasma hominis and Ureaplasma urealyticum were inoculated in A9 agar and tested with the Mycoplasma Kit (bioMeriéux, Marcy-l′Etoile, France). The culture was considered to be positive when ≥104 color-changing units (ccu)/mL were observed. During the period of study, Mycoplasma genitalium was not sought on a routine basis.
  • (4) Samples for Chlamydia trachomatis detection were taken with a plastic swab and tested for chlamydial lipopolysaccharide antigen by means of an enzyme immunoassay ([EIA] Chlamydiazime; Abbott Laboratories, Abbott Park, IL) and, after 1997, with polymerase chain reaction (Amplicor; PCR Diagnostic, Roche Diagnostic Systems, NJ) and ligase amplification reaction (LCx Chlamydia; Abbott Laboratories). We included testing for detection of syphilis (RPR, TPHA, and FTA), HIV (EIA and Western blotting), and genital herpes (direct IF; Syva Microtrack, Behring Diagnostics, Cupertino, CA) with a viral pack (Biomedics, Barcelona, Spain) and shell vial with immunofluorescence and conventional culture.

Tobacco use was defined as moderate at less than 20 cigarettes per day and high at more than 20 per day. 7,8 Alcohol intake was defined as at least 80 g per day for men and 20 g per day for women. 9

Statistical analysis was performed by means of chi-square tests, with Yates correction where appropriate. Values of P < 0.05 were considered to denote statistical significance.


In the period of study, a diagnosis of pubic lice was made in 197 cases (2.2%). There were 127 infested males (3.7%) and 70 infested females (1.2%); the male-to-female ratio was 1.8:1. Among men, more cases involved MSM (29 of 152 cases) than heterosexual men (98 of 3248 cases) (P < 0.001). The distribution by years, with a range of 1.3% to 4.6% per year, is shown in Table 1. The social and demographic factors of the cases and the control group are shown in Table 2. The age range in the index group was 15 to 69 years (mean, 30.3); there were 12 females (17.1%) and 25 males (19.7%) older than age 35 years. In 67.5% of the cases the patients were single. The type of sexual relationship was mainly sporadic in 40.1% and with a partner in 27.9%. Condoms were used by 34 patients (17.2%). There was a statistical difference between the index and control groups with regard to single status (P < 0.001) and more use of condoms (P < 0.01) among men with pubic lice. The seasonal distribution of cases was as follows: 45 in winter, 51 in spring, 45 in summer, and 56 in autumn.

Yearly Distribution of Patients With Pubic Lice
Social and Demographic Factors in Pubic Lice Cases and the Control Group

Table 3 shows the association of other STDs and genital microorganisms with pubic lice and in the control group. In males, the most frequent disease (31.4%) was urethritis (including ureaplasmal, chlamydial, trichomonal, and gonococcal urethritis), followed by candidal balanitis (7.1%); in females, the most frequent were vulvovaginitis (including candidiasis and trichomoniasis) and bacterial vaginosis (40%) and cervicitis (17.2). Pubic lice were associated with HIV antibodies in 9 patients (4.6%): 3 female intravenous drug users (IDUs, 2 of whom were female prostitutes), 2 MSM, and 4 IDU heterosexual men. There was a statistical differences between the index and control groups with regard to more VIH infections (P < 0.01) in women with pubic lice and more cases of genital candidiasis (P < 0.001), VIH infection (P < 0.01), genital warts (P < 0.001), and hepatitis C infection (P < 0.05) among men in the control group.

Other Sexually Transmitted Diseases and Genital Microorganisms Associated With Pubic Lice Cases and the Control Group

The most frequent clinical symptoms were itching in 151 patients (76.6%) and erythema in 84 patients (42.6%), and 34% of the known partners complained of clinical symptoms (Table 4). During the period of study, reinfestations occurred in 15 patients (7.6%; 14 males and 1 female): 13 patients twice, 1 patient three times, and 1 four times. Among men, there were more reinfestations in MSM (8 of 21 cases) than in heterosexuals (6 of 92 cases;P < 0.01). The reinfestations occurred in all patients more than 1 year after the previous episode.

Clinical Signs and Symptoms in the Patients With Pubic Lice

The pediculicide treatment was with lindane for 193 patients (98%) and with permetrine for 4 (2%). Treatment was successful for 196 of 197 patients (99.5%). One patient had pubic lice after the treatment with lindane.


Pthirus pubis is a specific parasite of humans, and although its transfer to a dog has been recorded, 10 it cannot survive off the host for more than 24 hours. 1 The pubic louse is spread primarily through close physical or sexual contact, with about 95% of sexual contacts becoming infested. 11 During the 1970s, there was an increase in Edinburgh (Scotland), with one case for each 9 of gonococcal disease in males and for each 18 in women. 12 Records of new cases seen at genitourinary medicine clinics in the UK showed an increase from 6168 cases in 1976 to 10,522 in 1986. 13 In Israel, pubic lice infestation increased from 7 per 1000 in 1977 to 14.9 per 1000 in 1983 and then declined to 4.6 per 1000 in 1987. 14 In the same country, Israeli soldiers showed a sharp decline, 13.6-fold, from the 1970s to the present day. 15 In a study of rape victims, Estrich et al. 16 found one case of pediculosis pubis among 124 women (0.8%).

These figures indicate the trend in infestation rates, but the actual number of infections could be much higher, as many are dealt with by family physicians or by self-medication. 1 In our country, the yearly distribution shows a stable number of patients, ranging between 1.3% and 4.7%, with a peak in the number of cases in 1991. In Britain, in the period of 1975 to 1986, the range was 1.4% to 1.9%. 13

Like other STDs, pubic lice can serve as a warning of the possible presence of other such diseases: 31.4% of the patients infested had other STDs. 17 In our study, 75.6% of patients either were infected with another genital microorganism or had another STD or both (46.7% had only another STD), and 4.6% had HIV antibodies. Reports on STDs in patients with pubic lice differ. Earlier studies documented a high prevalence among adults with pubic lice, although without statistical significance; Opayene et al. 18 found a higher prevalence in the control group and, in a recent study of adolescents, 19 a higher chlamydial infection in the index group than in the control group, although this study did not include a complete STD evaluation.

In our population, we found STDs more frequently in the index group but found STDs such as genital candidiasis and genital warts more frequently in the control group; the reasons for these findings are unclear. Very little has been written about the effect that HIV infection has on infestation with pubic lice, and it appears that the ectoparasites show the same clinical characteristics, regardless of HIV serostatus; the Center for Disease Control and Prevention recommends the same treatment regardless of HIV serostatus. 20 Our few patients infected with HIV exhibited the same clinical characteristics as non-HIV-infected patients, and one explanation is that pediculicide treatment efficacy is independent of the immunologic status of the patient.

Classic infection is confined to those of a low socioeconomic status 3 and frequently is associated with the presence of other sexually transmitted infections, as mentioned above; thus, these patients should be examined for such infections. 4 Risk factors for pediculosis pubis in women are pregnancy and age less than 25 years, and in men, lack of a steady partner, multiple partners, unmarried status, and homosexual behavior, 21 all of which can be considered sexual activity factors. In our series, the prototype patient was a single person who had sporadic sexual intercourse and did not use condoms. Of the males, 51.2% had a relationship with a female prostitute. There was no seasonal pattern in our cases, which contrasts with the results of other investigators, 14 who reported that this disease is more frequent in the cooler months of the year.

It has been stated that the population with the highest incidence of pubic lice is similar to that with the highest incidence of gonorrhea and syphilis—that is to say, persons aged 15 to 25 years—and that the prevalence declines gradually to age 35 years, after which infestation becomes rare. 5 Fisher and Morton 12 found infestation most commonly in women aged between 15 and 19 years and men more than 20 years old. Similarly, another study 22 demonstrated a higher prevalence (0.3%) in girls between 13 and 15 years old than in boys of the same age range (0.1%). However, the age distribution in our study was clearly different, since nearly 19% of the infested patients were older than age 35 years. This could be due to the influence of the Spanish population pyramid, with an aging population, as seen in few other parts of Europe.

These lice colonize the genital and inguinal regions but occasionally may colonize eyebrows, eyelashes, beard, axillae, areolar hair, and occasionally scalp hair, particularly the scalp margins. 23–36 A case of an associated inflammatory tubo-ovarian tumor has been described. 37 In heavy infections in men, the hair on the trunk and limbs may be extensively colonized, 38 and a case has been reported in which the presence of an enormous population of lice was attributed to inappropriate use of topical steroids. 39 Furthermore, pubic lice infestation could be a marker of sexual abuse. 40,41

In a study of 121 patients with pediculosis pubis, Chapel et al 17 noted the presence of the parasite in pubic hair in 118 patients. In 38 men (37.3%) and 18 women (94.7%), the pubic region was the sole area of involvement. Pruritus was reported by 104 patients (85.9%), while excoriations were observed in 30 (24.8%) and maculae cerulea in 1. In our patients the infestation was confined to the genital region, and the predominant symptoms were itching (76.6%) and erythema (42.6%). Because of the unspecific symptoms of this disease, we look for it actively in all patients attending the STD clinic. Superinfection was present in one patient (0.5%). During the period of study, 11% of the male patients (mainly MSM) had a reinfestation (P < 0.01), and reinfestation was more frequent than in females (P < 0.05).

Pediculosis pubis was associated in a previous study 21 with sexual activity factors, but the reason for the higher frequency in MSM than in the women prostitutes with multiple sexual contacts is not clear. The explanation may be socioeconomic, pharmacological, or environmental, or the higher frequency may be due to prevention policy modifications—the same factors that have been suggested by other authors as possible causes of the reduction in the prevalence of this disease. 15 One other possible explanation is that the female patients depilate more frequently than the men (65% versus 0%; data not shown), and the hairs are necessary to the lice.

One heterosexual male patient, who was negative for HIV antibodies, became reinfested immediately after the treatment with lindane. Resistance of head lice to lindane was reported in the United Kingdom in 1971 and in the Netherlands in 1978. Resistance develops easily when nymphs rather than adults are exposed, and it also occurs because of the use of inadequate quantities of the pediculicide, such as shampoo. 42 It seems probable that our patient's reinfestation was due not to failure of the pediculicide itself (treatment was successful for 99.5%) but to its incorrect application.

In conclusion, the data of recent years show that among our patients the incidence of infestation was stable during the period of study, with an older age range than reported previously, a high frequency of other associated STDs, and a statistically higher number of reinfestations in males than in females. The MSM were more frequently infested and reinfested than heterosexual men.


1. Champion RH, Burton JL, Burns DA, Breathnach SM, eds. Textbook of Dermatology. Vol. 2. 9th ed. Blackwell Science 1998: 1443–1444.
2. Burgess I. Human lice and their management. Adv Parasitol 1995; 36: 271–342.
3. Gillis D, Slepon R, Karsenty E, Green MS. Sociodemographic factors associated with pediculosis capitis and pubis among young adults in the Israel Defense Forces. Public Health Rev 1990–91; 18: 345–350.
4. Routh HB, Mirensky YM, Parish LC, Witkowski JA. Ectoparasites as sexually transmitted diseases. Semin Dermatol 1994; 13: 243–247.
5. Billstein SA. Pubic lice. In: Holmes KK, Sparling PF, Mardh P-A, et al, eds. Sexually Transmitted Diseases. 3rd ed. New York: McGraw-Hill, 1999: 641–644.
6. Murray PR, Baron EJ, Pfaller MA, et al, eds. Manual of Clinical Microbiology. 6th ed. Washington, DC: ASM Press 1995.
7. The Tobacco Use and Dependence Clinical Practice Guideline Panel, Staff, and Consortium Representatives. A clinical practice guideline for treating tobacco use and dependence: a US Public Health Service Report. JAMA 2000; 283: 3244–3254.
8. Raw M, McNeill A, West R. Smoking cessation guidelines for health professionals. A guide to effective smoking cessation interventions for the health care system. Thorax 1998; 53( Suppl 5): S1–S19.
9. Diehl AM. Liver disease in the alcoholic: clinical aspects. In: Zakim D and Boyer TD, eds. Hepatology. A textbook of liver disease. 3rd ed. Philadelphia: WB Saunders 1996: 1050–1060.
10. Frye FL, Furman DP. Phthiriasis in a dog. J Am Vet Med Assoc 1968; 152: 1113.
11. Letau LA. Nosocomial transmission and infection control aspects of parasitic and ectoparasitic diseases. Part III. Ectoparasites/summary and conclusions. Infect Control Hosp Epidemiol 1991; 12: 179–185.
12. Fisher I, Morton RS. Phthirus pubis infestation. Br J Vener Dis 1970; 46: 326–329.
13. Public Health Service Communicable Disease Surveillance Centre. Sexually transmitted diseases in Britain: 1985–6. Genitourin Med 1989; 65: 117–121.
14. Gillis D, Slepon R, Karsenty E, Green MS. Seasonality and long term trends of pediculosis capitis and pubis in a young adult population. Arch Dermatol 1990; 126: 638–641.
15. Mimouni D, Grotto I, Haviv J, Gdalevich M, Huerta M, Shpilberg O. Secular trends in the epidemiology of pediculosis capitis and pubis among Israeli soldiers: a 27-year follow-up. Int J Dermatol 2001; 40: 637–639.
16. Estreich S, Forster GE, Robinson A. Sexually transmitted diseases in rape victims. Genitourin Med 1990; 66: 433–438.
17. Chapel TA, Katta T, Kuszmar T, DeGiusti D. Pediculosis pubis in a clinic for treatment of sexually transmitted diseases. Sex Transm Dis 1979; 6: 257–260.
18. Opaneye AA, Jayaweera DT, Walzman M, Wade AAH. Pediculosis pubis: a surrogate marker for sexually transmitted disease. J R Soc Health 1993; 113: 6–7.
19. Pierzchalski JL, Bretl DA, Matson SC. Phthirus pubis as a predictor for chlamydial infections in adolescents. Sex Transm Dis 2002; 29: 331–334.
20. Czelusta A, Yen-Moore A, Van der Straten M, et al. An overview of sexually transmitted diseases. Part III. Sexually transmitted diseases in HIV- infected patients. J Am Acad Dermatol 2000; 43: 409–432.
21. Hart G. Factors associated with pediculosis pubis and scabies. Sex Transm Infect 1992; 68: 294–295.
22. Awahmukalah DS, Dinga JS, Nchako-Njikam J. Pediculosis among urban and rural school children in Kumba, Meme division, south-west Cameroon. Parasitologia 1988; 30: 249–256.
23. Velazquez CC. Phthirus pubis from human eyelashes in the Philippines. J Parasitol 1968; 54: 1140.
24. Elgart ML, Higdon RS. Pediculosis pubis of the scalp. Arch Dermatol 1973; 107: 916–917.
25. Mueller JP. Pubic lice from the scalp hair; a report of two cases. J Parasitol 1973; 59: 943–944.
26. Witkowski JA, Parish LC. Pthiriasis capitis. Int J Dermatol 1979; 18: 559–560.
27. Kirschner MH. Phthirus pubis infestation of the eyelashes. JAMA 1982; 248: 428.
28. Kincaid MC. Phthirus pubis infestation of the lashes. JAMA 1983; 249: 590.
29. Alexander JO. Phthirus pubis infestation of the eyelashes. JAMA 1983; 250: 32–33.
30. Chitchang S, Yodmani B. Phthiriasis capitis. J Med Assoc Thailand 1983; 66: 728–729.
31. Signore RJ, Love J, Boucree MC. Scalp infestation with Phthirus pubis. Arch Dermatol 1989; 125: 133.
32. Baker RS, Feingold M. Phthirus pubis (pubic louse) blepharitis. Am J Dis Child 1984; 138: 1079–1080.
33. Dornic DI. Ectoparasitic infestation of the lashes. J Am Optom Assoc 1985; 56: 716–719.
34. Silburt BS, Parsons WL. Scalp infestation by Phthirus pubis in a 6-week-old infant. Pediatr Dermatol 1990; 7: 205–207.
35. Singh S, Singh N, Ray JC, Roy S, Garg SP. Phthirus pubis infestation of the scalp: report of three cases. Rev Infect Dis 1990; 12: 560.
36. Rundle PA, Hughes DS. Phthirus pubis infestation of the eyelids. Br J Ophthalmol 1993; 77: 815–816.
37. Wierani F, Grin W, Grunberger W. Phthirus pubis as the cause of tubo-ovarian conglomerate tumor. Geburtshilfe Frauenheilkd 1993; 53: 721–723.
38. el-Sibae MM. Generalized pediculosis due to Phthirus pubis. J Egypt Soc Parasitol 1991; 21: 593.
39. Nielsen AO, Secher L. Pediculosis pubis in a patient treated with topical steroids. Cutis 1980; 25: 655–658.
40. Scott MJ, Esterly NB. Eyelash infestation by Phthirus pubis as a manifestation of child abuse. Pediatr Dermatol 1983; 1: 179.
41. Skinner CJ, Viswalingam ND, Goh BT. Phthirus pubis infestation of the eyelids: a marker for sexually transmitted diseases. Int J STD AIDS 1995; 6: 451–452.
42. Witkowski JA, Parish LC. Pediculosis and resistance: The perennial problem. Clin Dermatol 2002; 20: 87–92.
© Copyright 2003 American Sexually Transmitted Diseases Association