Several studies of individuals infected with Chlamydia trachomatis or Neisseria gonorrhoeae have found high proportions carrying both infections.1–13 Among individuals infected with gonorrhea, 20% to 57% of women1,3–13 and 3.3% to 37% of men2,6,9–11,13 were concurrently infected with chlamydia, and 4.3% to 31% of women1,4,5,7,8,11 and 12% to 28% of men11 infected with chlamydia were concurrently infected with gonorrhea. Variations in coinfection rates in these reports may be attributed partly to differences in the methods used for disease detection and the sizes and characteristics of the populations studied. Included in these investigations were patients seeking care in adolescent clinics,1,4,8 prenatal clinics,3,12 family planning clinics,5,12 school-based health centers,7 or genitourinary medicine/sexually transmitted diseases (STD) clinics.2,6,9–13 Adolescents infected with chlamydia or gonorrhea in these clinic settings have had higher rates of co-infections compared to individuals in older age groups.9–12
Because many infections with chlamydia and gonorrhea remain asymptomatic, high numbers of infected individuals may not seek care.14 This probably contributes to the less well-known co-occurrence of chlamydia and gonorrhea outside of healthcare facilities. Chlamydia and gonorrhea co-infection among unselected adolescents screened in a community-based setting has not been described. We report on the co-occurrence of both infections among high school students who were simultaneously tested for chlamydia and gonorrhea in an urban United States school district, and seek to characterize those with dual infection. Because the Centers for Disease Control and prevention (CDC) estimate that dual treatment without testing for chlamydia is cost-effective for populations in which co-infection with chlamydia occur in 10% to 30% of gonorrhea infections,15 we also assessed the relevance of the CDC dual treatment recommendations in this student population.
During the school year 1998 to 1999, 6,020 students participated in the fourth year of a school-based STD screening offered every year in the school district since the 1995 to 1996 school year.16 The school-based STD screening, including consent solicitation, screening procedures, counseling and treatment of infected subjects, and partner notification and referrals have been described previously.16,17 Approval for the screening program was obtained from the school district and the appropriate university Institutional Review Board.
Before the screening, demographic information of all students enrolled in the participating schools, including date of birth, gender, race/ethnicity and grade, was obtained from the schools administrative offices. All students were then assigned a code number that was used to identify laboratory specimens and to provide test results to those who participated. Only students who obtained consent from their parents/guardians or were 18 years of age or older and consented for the STD testing could participate. At the time of the screening, students who had consent and were willing to participate were asked in a face-to-face interview whether they currently had any symptom of STD (e.g., genital discharge or itching, burning or pain during urination). No sexual behavior questions were asked. Each participant provided a urine specimen that was tested for both C trachomatis and N gonorrhoeae using the ligase chain reaction DNA amplification assays, following manufacturer’s instructions (LCx Probe System; Abbott Laboratories, Abbot Park, IL). The laboratory made both test results available approximately 5 working days after specimen collection. All positive test results were reported to the State Health Department.
Students infected with both chlamydia and gonorrhea were compared to those infected with only 1 of the 2 STDs using chi-squared and F tests for categorical and continuous variables respectively, with all P values less than 0.05 considered statistically significant.
The 6,020 students tested were in grades 7 to 12 and aged between 12 and 22 years. The current analysis was restricted to 5,877 participants in grades 9 to 12 and whose ages ranged from 14 through 20 years (97.6% of all those screened). They were 95.9% black, 51.2% males, and their mean age was 16.52 ± 1.35 years (median = 16.00 years). The 143 students not included in this analysis (2.4%) were either in seventh or eighth grades, aged less than 13 or more than 20 years, of them none had dual infection.
Overall, 401 students tested positive for chlamydia only, 67 tested positive for gonorrhea only, and 50 tested positive for both STDs, leading to 451 students (7.7%) testing positive for chlamydia and 117 students (2.0%) testing positive for gonorrhea (Table 1). The gonorrhea coinfection among students who had chlamydia was 50/451 (11.1%), 14/154 (9.1%) for males and 36/297 (12.1%) for females (P > 0.33); the chlamydia coinfection among students who had gonorrhea was 50/117 (42.7%), 14/30 (46.7%) for males and 36/87 (41.4%) for females (P > 0.61). Rates of co-infections among students who reported STD symptoms were significantly higher (P < 0.01) than among students who did not report symptoms. Differences in coinfection rates by age and by grade were not statistically significant (data not shown).
All 518 students with positive STD test results were black except 2, who were Hispanic. Students who had chlamydia only or gonorrhea only did not differ from those who had dual infection with regard to gender, age and grade distributions (Table 2). Of the 514 students with positive STD test results and symptom information, 481 (93.6%) reported no symptom. However, symptoms of STDs were reported by 16.0% (8/50) of students who had both infections, 7.7% (5/65) of students who had gonorrhea only, and 5.0% (20/399) of students who had chlamydia only (P = 0.01) (Table 2). When analyzed separately for each gender, STD symptoms were reported by 21.4% (3/14) of males and 13.9% (5/36) of females who had both infections, 20.0% (3/15) of males and 4.0% (2/50) of females who had gonorrhea only, and 4.3% (6/140) of males and 5.4% (14/259) of females who had chlamydia only.
Consistent with previous studies, we found high proportions of individuals carrying both chlamydia and gonorrhea among those infected with either of the 2 STDs. Also as in almost all studies that reported coinfection rates in both directions,1,4,5,7,8,11 the chlamydia co-infection among individuals infected with gonorrhea was higher than the gonorrhea co-infection among individuals infected with chlamydia. Students who had both infections were similar to those who had either infection alone in terms of gender, age, and grade characteristics. However, STD symptoms were reported more frequently by students who had both infections compared to those who had either infection alone.
Among patients seen in STD clinics, chlamydia and gonorrhea coinfection has been found significantly more frequently among females compared to males.6,9,10,13 In our study, no statistically significant gender differences in coinfection rates were found, although the prevalence for chlamydia was twice and that for gonorrhea 3 times as high among females as among males.16 Recently, data have shown that higher or lower overall prevalences for chlamydia and gonorrhea do not necessarily translate into correspondingly higher or lower prevalences of coinfection among those carrying either STD.12,13
Symptom information was obtained by face-to-face interviewing, which may result in biased responses from participants. In addition, symptoms reported are not specific to chlamydia or gonorrhea. However, the finding that symptoms related to STDs were reported more frequently by co-infected students than those with one infection could be attributed to a greater inflammatory response occurring with dual infection as opposed to one infection, and lends some support to the validity of self-reported symptoms among students infected.
We universally screened non-healthcare-seeking adolescents using nucleic acid amplification tests (NAATs) to detect both STDs in a single laboratory specimen. Therefore, our findings may differ from those of other previous studies owing to differences in disease detection methodology and population sampling. Studies by Burstein and colleagues7 and Xu and colleagues8 utilized NAATs to detect both STDs among sexually active female adolescents seeking care in school-based health centers and adolescent clinics. Hijazi and colleagues,9 Creighton and colleagues11 and Lyss and colleagues13 utilized NAATs only to detect chlamydia but not gonorrhea, among patients seeking care in STD clinics. Other studies1–6,10,12 utilized culture and non-amplification methods to detect both STDs, techniques that have been found to be less sensitive compared to NAATs.8,18–20 Thus, our study extends the literature on chlamydia and gonorrhea co-infection and differs from other previous studies in both study population and STD detection methodology.
Limitations of our study include the inability to generalize our findings to adolescents not attending schools, to high school students in other geographic locations or of predominantly non-black student body, and to other high-risk populations not seeking care. Because only one half of the entire school population participated in the screening,16 findings may not apply to students who did not participate. The temporal sequence in the acquisition of dual infection among co-infected students cannot be determined because the screening was cross-sectional. Results from this study cannot be directly compared with those from other previous studies of chlamydia and gonorrhea co-infection because of differences in study populations and STD detection methodology.
Studies of concomitant STDs have contributed knowledge to guide patient management including treatment, education, and counseling. For example, recommendations that patients treated for gonorrhea be also given an effective treatment against chlamydia are based on observations that patients infected with gonorrhea often are co-infected with chlamydia.15 Among our high school students, 41% of females and 47% of males infected with gonorrhea were co-infected with chlamydia, exceeding the 10%-30% co-infection rates that make co-treatment in patient-care settings cost-effective.15 Clearly, dual treatment for chlamydia without testing among individuals infected with gonorrhea is justified in this population by CDC standards. But, because this population was not attending healthcare settings and was less likely to receive STD testing under routine healthcare practice, obviously, the gonorrhea infection that would trigger dual treatment for chlamydia was unlikely to be detected.
Because the gonorrhea infection status of the participant was unknown at the time of specimen collection, because treatment decisions without laboratory test results could not be made, and because both chlamydia and gonorrhea test results later became available at the same time, presumptive treatment for chlamydia could not be applied in this setting. With NAATs increasingly leading to the implementation of STD screenings outside of traditional clinical settings, dual treatment without testing for chlamydia among populations in which co-infection may be sufficiently high is less likely to apply where no treatment decisions can be made without STD test results and chlamydia and gonorrhea test results are likely to be available when any treatment can be administered.
The prevalence of STDs in our high school student population is high enough to justify screening for chlamydia.16,17,21 The chlamydia and gonorrhea co-infection among these apparently healthy adolescents who were offered STD testing at their schools during regular school hours should raise awareness of chlamydia and gonorrhea co-occurrence among certain high-risk populations outside of patient-care settings. For such populations, this study suggests that in this era of STD detection capabilities using laboratory specimens that can be obtained without the performance of a physical examination,8,18–20 simultaneous screening for both chlamydia and gonorrhea remains the first line for intervention and action.
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