confirmatory testing of naats should be routine for chlamydia infections in populations with < 4%...
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Confirmatory Testing of NAATs SHOULD be Routine for Chlamydia Infections in Populations with < 4% Prevalence
Harold C. Wiesenfeld, M.D.,C.M.
University of Pittsburgh School of Medicine
Magee-Womens Hospital
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Positive Predictive Value:The Influence of Disease Prevalence
Zenilman. Sex Transm Infect 2003
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Positive Predictive Value:The Influence of Disease Prevalence
PPV at Specificity of:
Prevalence 98% 99% 99.5%
10% 84% 91% 95%
5% 71% 83% 90%
2% 49% 66% 79%
1% 32% 49% 66%
0.5% 19% 32% 49%
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Positive Predictive Value:The Influence of Disease Prevalence
95% Sensitivity 99% Specificity
Prevalence Test True Infection PPV
+ -
10% + 95 9 104 91%
- 5 891 896 (95/104)
100 900 1000
4% + 38 10 48 79%
- 2 950 952 (38/48)
40 960 1000
2% + 19 10 29 66%
- 1 970 971 (19/29)
20 980 1000
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BD ProbeTec PerformanceMulticenter Evaluation
Female Swab Male Swab
Lab Prevalence SPEC PPV SPEC PPV
IU 13.4% 95.7 76.8 96.1 86.8
JHU 9.0% 99.0 87.4 98.1 92.1
UCSF 5.3% 100 100 100 100
SJPHS 4.4% 99.2 84.6 - -
UAB 15.1% 98.6 92.1 95.2 86.3
UMMS 10.9% 98.6 77.7 80.0 50
CCF 11.5% 95.7 75.1 - -
Van Der Pol et al. J Clin Micro 2001
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LCR PerformanceMulticenter Evaluation
Female Swab Male Urine
Lab Prevalence SPEC PPV SPEC PPV
IU 13.4% 98.8 92.5 97.0 89
JHU 9.0% 99.0 85.6 96.2 85.4
UCSF 5.3% 100 100 100 100
SJPHS 4.4% 99.4 88.5 - -
UAB 15.1% 99.3 95.9 95.2 97.3
UMMS 10.9% 98.5 89.1 80.0 66.7
CCF 11.5% 100 100 - -
Van Der Pol et al. J Clin Micro 2001
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Reproducibility of BD Probe-Tec
Initial MOTA Scores
2,000-9,999 >10,000
Repeat Positive
21 175
Repeat Negative
5 6
Total 26 181
Culler. J Clin Micro 2003
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Implications of a Positive CT Test
• Psychosocial Impact/Stigma
• Negative impact on sexual relationships
• Future Reproductive Morbidity
• Cost
• Resource Utilization
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Implications of a Positive CT Test
• Psychosocial Impact– Shock– Depression– Anxiety– Guilt– Isolation– Shame– Stigma (?barrier to future STD care?)
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Implications of a Positive CT Test
• Negative impact on sexual relationships– Destroyed relationships– Accusations of infidelity– Impaired intimacy– Less sexually desirable– Less sexual enjoyment
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Implications of a Positive CT Test
• Future Reproductive Morbidity– Increased risk of
• Ectopic pregnancy• Tubal factor infertility• Chronic pelvic pain
– Neonatal transmission
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Implications of a False-Positive CT TestShort-Term Costs
Confirmatory Testing
Additional assay• Small # of specimens in
low prev. populations
• Lab issues
No Confirmatory Testing
TreatmentPartner notificationPartner treatmentScreening for other STDsCounseling time
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Implications of a Positive CT TestLong-Term Costs
Resource Utilization
• False positive tests will lead to increased utilization of healthcare services ($$$)– Repeat screening for C. trachomatis
• Follow national screening recommendations
– Increased healthcare utilization• Patient is “labelled”• All pelvic pain = PID (costs of treatment)• Increased surveillance for ectopic pregnancy
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Implications of a False-Positive CT TestOverall Costs
Confirmatory Testing
Additional assay
No Confirmatory Testing
TreatmentPartner notificationPartner treatmentScreening for other STDsCounseling timeRepeat testingFuture testing and work-up for
possible STD-related illness (e.g. PID, ectopic pregnancy)
Reduce costs
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Is Educating Physicians on the Proper Interpretation
of STD Tests a
Viable Strategy?
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Will Providers Properly Counsel Patients?
• 71% of PA primary care physicians report adequate STD training in residency (Ashton, Cook, Wiesenfeld et al. Sex Transm Dis 2002)
• 38% of adults were asked about STDs during routine checkups in the last year (Tao, Irwin & Kasler Am J Prev Med 2000)
• Only 32% of primary care physicians report screening a sexually active teen for CT (Cook, Wiesenfeld, Ashton et al. J Adol Health 2001)
• Only 61% of PCPs met criteria for adequate STD knowledge (Wiesenfeld, Cook et al. Unpublished data)
QUALITY OF STD CARE VARIES AND IS IMPERFECT
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“Clinicians must know the approximate prevalence of the condition of interest in the population being tested; if not, reasonable interpretation is impossible”
David A. Grimes & Kenneth F. Shulz
Uses and Abuses of Screening Tests
Lancet 2002
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What do the Providers Know About False Positive STD Tests?
• NOT MUCH!• Survey of local providers:
– 94% underestimated the false-positive rate of a NAAT CT test in a low prevalence population
– Most physicians vastly underestimated the false positive rate of CT NAAT testing:• Two-thirds estimated the false positive rate of
< 5% in a population where the risk of a positive test being a false positive is 50%
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Do Physicians Currently Follow Recommendations Concerning False-Positive Tests?
CDC (MMWR Oct 18, 2002):
“Patients with positive screening test results require counseling regarding…the possibility of a false-positive result”
Survey:
76% of physicians rarely (<1%) inform patients with a positive CT NAAT result that it may be a false positive
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Do Physicians Currently Follow Recommendations Concerning False-Positive Tests?
CDC (MMWR Oct 18, 2002):
“Because therapy for CT is safe and should not be delayed, therapy can be offered while awaiting additional test results…”
Survey:
18% of physicians would offer empiric treatment before or in lieu of retesting
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Is Educating Physicians on the Proper Interpretation
of STD Tests a
Viable Strategy?
Doubtful
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Should Confirmatory Testing of NAATs be Routine for Chlamydia Infections in Populations
with < 4% Prevalence?
YES• Not labor intensive• Additional costs small (small #s)• Reduction in costs incurred with false-positive
tests (short and long-term)• Eliminate unnecessary adverse psychosocial
impact• Feasibility of providers incorporating counseling
on false-positive results is questionable• Improved quality of care for our patients
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“ Remember: a clinician, not a laboratory test, makes a diagnosis. Overinterpretation of test results is the first cost of molecular diagnostics”
Jeffrey Klausner, MD
Clin Infect Dis 2004