Outcome | Risk for Chlamydia trachomatis Infection | |||
---|---|---|---|---|
Low | Moderate | Moderate to High | High | |
Epidemiologic | ||||
Prevalence, % | 0.1 | 1 | 5 | 10 |
New cases, n | 10 | 100 | 500 | 1000 |
Expected PID in untreated C. trachomatis rateb | 0.3 | 0.3 | 0.3 | 0.3 |
Expected cases of PID in untreated women without screening, n | 3 | 30 | 150 | 300 |
Screening | ||||
Urine nucleic acid amplification test | ||||
Sensitivity | 0.9 | 0.9 | 0.9 | 0.9 |
Specificity | 0.99 | 0.99 | 0.99 | 0.99 |
Screening results, % | ||||
True positive | 9 | 90 | 450 | 900 |
False negative | 1 | 10 | 50 | 100 |
False positive | 100 | 99 | 95 | 90 |
Total positive | 109 | 189 | 545 | 990 |
Positive predictive value, % | 8.25 | 47.6 | 82.3 | 90.9 |
Effect of therapy | ||||
Adherence to azithromycin therapy | 0.8 | 0.8 | 0.8 | 0.8 |
C. trachomatis infection treatedc | 7.2 | 72 | 360 | 720 |
C. trachomatis infection cured with treatment | 0.96 | 0.96 | 0.96 | 0.96 |
Cases of C. trachomatis infection cured | 6.9 | 69 | 345.6 | 691.2 |
Cases of C. trachomatis infection not cured | 0.3 | 3 | 14.4 | 28.8 |
Total cases of C. trachomatis infection after screening and treatmentd | 1.3 | 13 | 64.4 | 128.8 |
PID | ||||
Expected cases with screening, n | 0.39 | 4 | 19 | 39 |
Cases avoided by screening, n | 2.6 | 26 | 131 | 261 |
Number needed to screen to avoid 1 case of PID | 3846 | 384.6 | 76.3 | 38.3 |
Infertility | ||||
Expected cases resulting from C. trachomatis infection-related PID, n | 0.08 | 0.8 | 3.8 | 7.8 |
Cases avoided by screening, n | 0.52 | 5.2 | 26.2 | 52.2 |
Number needed to screen to avoid 1 case of infertility | 19 231 | 1923 | 382 | 192 |
Notes:
a. Assumptions made in this table,
which are derived from a review of the literature by Hu and colleagues24
include that 80% of women with a positive result on chlamydia
testing will be contacted and will receive and take azithromycin; 96% of women
treated with azithromycin will be cured of infection; and 20% of women who
experience PID will become infertile. PID = pelvic inflammatory disease.
b. Back from reference 1.
c. True-positive rate multiplied by 0.8.
d. Persons with a false-negative rate plus persons
in whom infection is not cured.