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Table 2. Balance Sheet: Screening for Chlamydia in 10,000 Women Aged 18-34 Years
| |
Low risk
(questionnaire)a |
Low risk
(no questionnaire)b |
High riskb |
|---|
| Base case assumptions |
|
Prevalence of chlamydia in population |
0.03 |
0.03 |
0.094 |
| Compliance with chlamydial testing |
0.64 |
0.64 |
0.64 |
| Sensitivity of test |
100% |
100% |
100% |
| Results |
| Mailed questionnaire |
10,000 |
|
|
| Responded to questionnaire |
5,701 |
|
|
| Identified as high-risk |
713 |
|
|
| Prevalence in risk group |
0.07 |
0.03 |
0.094 |
| Tested for chlamydia |
457 |
6400 |
6400 |
| Cases of chlamydia diagnosed and treated |
32 |
192 |
602 |
| Cases of pelvic inflammatory disease prevented |
9 |
53 |
167 |
| Number needed to screen (using questionnaire) to prevent one case of pelvic inflammatory disease |
1,130 |
not applicable |
not applicable |
| Number needed to invite for screening (using chlamydial test) to prevent one case of pelvic inflammatory disease |
81 (57)c |
188 (120) |
60 (39) |
[a] Assumptions based on the results of a randomized controlled trial conducted at Group Health of Puget Sound46 described in the text.
[b] Assumptions based on theoretical populations. The proportion of all patients who meet the criteria for "high risk" varies with practice setting, patient population, and the criteria used to define high risk.
[c] Numbers in parentheses indicate number needed to screen based on actual number of women tested for chlamydia. |
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