Screening for Chlamydial Infection: An Evidence Update. Table 2

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Table 2. Outcomes of Screening 10 000 Asymptomatic Women for Chlamydial Infection^a

Outcome	Risk for Chlamydia trachomatis Infection
Outcome	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 rate^b	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 treated^c	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 treatment^d	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.

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Table 2. Outcomes of Screening 10 000 Asymptomatic Women for Chlamydial Infectiona

Table 2. Outcomes of Screening 10 000 Asymptomatic Women for Chlamydial Infection^a