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Phthirus pubis in a Sexually Transmitted Diseases Unit

A Study of 14 Years

VARELA, JOSÉ A. MD*; OTERO, LUIS MD, PhD; ESPINOSA, EMMA MD; SÁNCHEZ, CARMEN*; LUISA JUNQUERA, MARÍA MD§; VÁZQUEZ, FERNANDO MD, PhD∥¶

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Sexually Transmitted Diseases: April 2003 - Volume 30 - Issue 4 - p 292-296
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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.

Results

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.

TABLE 1
TABLE 1:
Yearly Distribution of Patients With Pubic Lice
TABLE 2
TABLE 2:
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.

TABLE 3
TABLE 3:
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.

TABLE 4
TABLE 4:
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.

Discussion

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.

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