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Phthirus pubis as a Predictor for Chlamydia Infections in Adolescents


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Sexually Transmitted Diseases: June 2002 - Volume 29 - Issue 6 - p 331-334
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THE ORGANISM RESPONSIBLE for pubic lice infestation, Phthirus pubis, remains a common sexually transmitted infection (STI). P pubis is transmitted primarily through sexual contact, yet it is often overlooked in a discussion of STIs. Individuals infected with pubic lice have pruritus and pubic itching caused by lice secretions and excretions on the skin. 1 However, the more critical threat to these individuals may be concurrent infection with other, less obvious STIs. Pubic lice infestation is common in the United States and Western Europe, especially in the young, unmarried, sexually active segment of the population. 1 The population in which the incidence of pubic lice is highest is similar to that for gonorrhea and syphilis: single persons aged 15 to 25 years. 2

Previous studies have demonstrated concurrent gonorrhea and chlamydia infections in adults with pubic lice. This implies that pubic lice infestation may be a predictor for other STIs. For example, a 1970 study conducted by researchers in the United Kingdom showed that 28% of patients with pubic lice had concurrent gonorrhea. 3 Past studies have included varying percentages of adolescent subjects within adult populations; however, none focused specifically on the adolescent age group. Because adolescents remain the age group at greatest risk of contracting STIs, it is important to determine whether pubic lice represent a predictive factor for common infections such as gonorrhea and chlamydia.

Adolescents examined at urban juvenile detention centers are considered a high-risk population for all STIs because of socioeconomic status and behavioral risk factors. Several studies have documented that youths detained at these facilities are commonly noted to have STIs. Researchers in New York City found that 6% of detained youths were infected with gonorrhea and 5% had scabies or lice. 4 Our own data on youths admitted to the Milwaukee County Juvenile Detention Center reveal that 17% of youths tested for STIs are positive for chlamydia, 10% for gonorrhea, and 3% for pubic lice. 5

Anecdotally, we noted that detained youths with pubic lice infestation also had a high rate of other STIs. Identifying risk factors and predictive tools is imperative to achieving lower rates of STIs in high-risk adolescent populations. The aim of this retrospective study was to ascertain whether P pubis infestation was significantly associated with concurrent gonorrhea and/or chlamydia infections in the adolescent population examined at this facility.


This was a retrospective chart review designed to compare the prevalence of gonorrhea and chlamydia infections in sexually active adolescents with or without pubic lice infestation. The study protocol received approval from the Research and Publications Committee/Human Rights Review Board of the Medical College of Wisconsin/Children’s Hospital of Wisconsin. Subjects included adolescents who were examined at an urban juvenile detention center in Milwaukee, Wisconsin, between July 1998 and June 2000. All detained youths underwent an initial health screening on admittance to the facility, at which point treatment and testing were offered and follow-up care was recommended. The index group included all 62 adolescents with diagnosed P pubis infestation and subsequently screened for gonorrhea and chlamydia within the specified period. Diagnosis of pubic lice was based on visual observation of P pubis or their nits in sites of predilection. Controls included 201 sexually active detained adolescents without pubic lice who underwent screening for gonorrhea and chlamydia. Controls were randomly selected from 719 adolescents meeting the above criteria by way of a random number table. Gonorrhea was diagnosed with urine ligase chain reaction (LCR) or culture on modified Thayer–Martin medium. Chlamydia was diagnosed with urine LCR or enzyme immunoassay of cervical swabs.

A data sheet was developed in order to extract information from each subject’s medical chart. Data were collected on demographics, pubic lice infestation, subjective STI history, perceived symptoms at the time of evaluation, perceived substance and contraceptive use, and gonorrhea and chlamydia infection status. Data were entered into a statistical database (SPSS-PC; SPSS, Chicago, IL), and initial calculations such as for percentages, rates, means, and standard deviations were performed. Statistical significance was ascertained for an assortment of variables by means of t tests, chi-square analysis, and regression analysis. Statistical significance was evaluated on the basis of α = 0.05 and β = 0.2.

Subjects ranged in age from 13 to 18 years, with an average (SD) age of 15.9 ± 1.0 years. Most subjects were male (84%) and black (83%); there were few white (10%) and Hispanic (5%) youths. There were no statistically significant differences between the index and control groups with regard to demographics, STI history, perceived symptoms, and perceived substance and condom use.


Pubic Lice Infestation

Of those adolescents with diagnosed pubic lice, both lice and nits were found on 42% of subjects examined; 39% of subjects had lice only. Pubic lice nits alone were found on 18% of infected youths.

Sexual History of Adolescent Youths

Many youths (17%) reported a history of STI, including 13% of index subjects and 18% of control subjects. Symptoms of an STI were reported by 18% of all subjects (24% of index and 16% of control subjects) at the time of examination. The most common symptom present at the time of examination was pubic itching, which occurred more frequently in the lice-infected index group (19% index and 4% control [P = 0.00008; odds ratio, 6.65; 95% CI, 2.28–19.87). Dysuria (3% index and 7% control) and urethral discharge (2% index and 7% control) showed a similar incidence. There was no statistical difference between index and control groups with regard to history of STI or symptoms of STI at the time of examination (Figure 1A).

Fig. 1
Fig. 1:
(A) Sexual history of lice-infested subjects and controls (NS = not significant). (B) Concurrent chlamydia and gonorrhea infections in lice-infested subjects and controls.

Perfect condom use (100% of all sexual contact) was reported by only 35% of subjects. Overall, the mean percentage of condom use was 72% (index and control group use: 66% and 74%, respectively). There was no statistical difference in condom use between the two groups (Figure 1A).

Concurrent Infections

There were 60 cases of chlamydia (23% of all youths) and 29 cases of gonorrhea (11%) in the entire study population. Figure 1B shows that concurrent chlamydia infection was noted in 39% of subjects with pubic lice, compared with 18% of control subjects (P ≤ 0.001). Gonorrhea was present in 18% of subjects with pubic lice, compared with 9% of control subjects, values that were not significantly different (P ≤ 0.54). Logistic regression was used to estimate the probability of positivity for chlamydia or gonorrhea when one or more of the predictor variables were present. Fifteen variables were entered by a forward stepwise method. The model for chlamydia included only concurrent diagnosis of pubic lice, history of STI, and diagnosis of gonorrhea. Thus, pubic lice infestation, gonorrhea, and a history of STI each predicted chlamydia infection in this study population (Table 1). The remaining 12 variables—sex, age, symptoms, dysuria, frequency of urination, urethral discharge, vaginal discharge, pubic itching, condom use, and use of cigarettes, alcohol, and marijuana—did not significantly predict chlamydia infection. The model that predicted gonorrhea included only urethral discharge, and concurrent chlamydia infection (Table 1). Thus, pubic lice infestation did not predict concurrent gonorrhea in this study.

Table 1
Table 1:
Logistic Regression Model of Factors Predictive of Concurrent Chlamydial Infections or Gonorrhea


To the best of our knowledge, this is the first study to document that pubic lice infestation is predictive of concurrent chlamydia infection in adolescent youths. The prevalence of concurrent chlamydia infection in this study is higher than prevalence rates documented in previous research in adults. A study conducted in the United Kingdom (1993) at a hospital genitourinary department showed that 13% of patients with pubic lice and 15% of patients without pubic lice tested positive for chlamydia. 6 The higher rate of concurrent chlamydia infection in our adolescent population may reflect the higher rates of STIs in this age group, improved testing techniques, and the high rates of sexual activity and infrequent condom use reported by this young population.

Previous studies have demonstrated a significant incidence of concurrent STIs in adults with diagnosed pubic lice. For example, a study conducted in the United Kingdom (1970) showed that 38% of patients with pubic lice had single or multiple coexisting STIs. Specifically, 28% had concurrent gonorrhea, 8% had trichomonas infection, 3% had nongonococcal urethritis, and 3% had scabies; the remaining cases included genital warts, candidiasis, and syphilis. 3 A 1979 study conducted in Detroit, Michigan, showed that 31% of patients with pubic lice had single or multiple concurrent infections such as gonorrhea (19%), nongonococcal urethritis (10% of males), trichomoniasis (11% of females), nonspecific vaginitis (11% of females), herpes (2%), and hepatitis B (1%). 7 A 1981 study conducted at a clinic in Copenhagen, Denmark, showed concurrent STIs, including gonorrhea (15% of women, 7% of men) and syphilis (2% of men), in patients with pubic lice. 8

Opaneye and colleagues 6 were the first to use a control group in order to compare the prevalence of various STIs in patients with or without pubic lice. This study was of patients presenting to a genitourinary clinic in Coventry, England. Although their ages were not stated in the article, the 140 lice-infested patients (115 males and 42 females) likely were adults. The prevalence of STIs in the control group in that study (51%) was surprisingly higher than that in the index group (37%). Specifically, diagnoses for patients in the control group were genital warts (21%), chlamydia (15%), nonspecific urethritis (7%), genital herpes (6%), and gonorrhea (1%). Thus, although earlier studies have documented a significant prevalence of STIs among adults with pubic lice, none have statistically determined pubic lice to be predictive of any STI in the adult population.

The results documented in the current study vary considerably from those of past studies. First, statistical evidence from this study reveals that pubic lice infestation predicts chlamydia infection in adolescents. In addition, the rate of gonorrhea among adolescents with pubic lice was twofold that among adolescents without pubic lice (18% versus 9%) This apparent difference requires further attention because a higher rate of concurrent gonorrhea was not demonstrated in adult populations in the past. Conversely, Opaneye et al. 6 detected gonorrhea in 4.1% of index subjects, versus 1.4% of control subjects, in a study of 285 adults.

The differences between the results of our study and those described in earlier reports may reflect variances in subjects’ ages or behavioral risk factors. For instance, this study focused on detained adolescents rather than adults at an STI clinic or hospital. The adolescent population is determined to be highly sexually active, often with multiple contacts. In addition, our population reported inadequate condom use (mean frequency of condom use: 72%), putting them at higher risk for STIs. Thus, the incidence and profile of STIs in the adolescent population of this study may be quite different from that in the adult population, and the correlation with lice infestation also may differ.

Of the subjects with pubic lice, only 24% reported symptoms at the time of examination, and pubic itching was reported by 19% of our youths. Other researchers have shown this to be a consistent motivating factor for patients with pubic lice infestation to seek medical treatment. 3,7 Symptoms suggestive of a concurrent STI (chlamydia or gonorrhea) were rare in those youths with pubic lice. Excluding pubic itching (reported by 19% of index subjects), symptoms of other STIs were reported by fewer than 5% of adolescents with pubic lice. For example, only 3% of subjects with lice reported dysuria, 17% of females noted vaginal discharge, and only 2% of subjects had urethral discharge. Thus, the current study documents that in this adolescent population, most of the infections coexisting with pubic lice are asymptomatic, which may lead them to be overlooked by clinicians unaware of the predictive value of pubic lice for STIs. Thus, the opportunity to identify and treat asymptomatic infections may be missed.

This study was limited by the retrospective design. Potential problems include bias, especially in the selection of control subjects. The criteria for screening youths for STIs may have varied over the 2-year period. Although previous studies have documented increased rates of STIs (other than gonorrhea and chlamydia) among patients with pubic lice infestation, this study did not include a complete STI evaluation for each subject. Although it clearly provides evidence that the presence of pubic lice is a predictor of chlamydia infections, the current study lacks sufficient numbers of index subjects to allow a full statistical analysis of the value of pubic lice infestation as a predictor of gonorrhea. Although this was not a statistically significant factor, 18% of the index group tested positive for gonorrhea, whereas gonorrhea was detected in 9% of the control group. At this rate of infection, a sample size of at least 155 cases of lice would be required for this difference to be statistically significant. Thus, the number of lice cases in this 2-year study (62) limited our ability to show a significant relationship between lice and gonorrhea, but our findings suggest the need for an expanded study to evaluate lice infestation as a possible predictor of this STI.

This study did not include many other risk factors (such as number of partners or exchange of sex for money) that may also have been predictive of concurrent STIs, because this aspect was beyond the scope of the research project. Finally, future prospective studies involving larger sample sizes and examinations that are more comprehensive will need to be completed to fully elucidate the relationship between pubic lice infestation and other STIs.

Populations in which documented prevalence rates are considerably higher than community norms (such as the youths in this study) should be screened and treated for all STIs. Unfortunately, the funds and personnel at most detention centers are simply insufficient to provide universal screening for the thousands of youths who pass through these facilities. In an effort to identify the youths at highest risk, our study clearly indicated that screening for concurrent STIs (specifically, chlamydia) is critical for adolescents infested with P pubis. Furthermore, considering the high prevalence of concurrent STIs in this population, we would advocate empirical treatment of all detained youths with pubic lice for both chlamydia and gonorrhea. 9 Many adolescents are released from detention before STI screening results are available. In the event of positive laboratory findings, adolescents must subsequently be located and convinced to seek treatment for concurrent infections, which are often asymptomatic. This process is difficult and does not ensure proper treatment for STIs. Untreated STIs lead to spread of the infection throughout the population as well as more serious complications of chronic infection such as epididymitis, prostatitis, and pelvic inflammatory disease. Therefore, it is reasonable to suggest empirical single-dose treatment (e.g., 400 mg cefixime and 1 g azithromycin orally) for gonorrhea and chlamydia infections in all detained youths with pubic lice. Recognizing pubic lice as a predictor of concurrent STIs in the adolescent population may permit immediate treatment that will help to lower the frequencies of gonorrhea and chlamydia infection in this high-risk adolescent population.


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© Copyright 2002 American Sexually Transmitted Diseases Association