Costeffectiveness of alternative strategies for tuberculosis screening before kindergarten

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Cost-effectiveness of alternative strategies for
tuberculosis screening before kindergarten

• Valerie Flaherman, M.D., M.P.H.
• University of California, San Francisco
• December 17, 2007

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Possible TB screening strategies for
pre-kindergarteners

• Universal tuberculin skin testing (TST)
• Universal risk factor screening followed by TST
  targeted only to children with a risk factor
  identified
• No screening mandated by health officers

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True-positives and false-positives by population
prevalence
(assuming 99 specficity), adapted from Table 6,
Diagnostic Standards and Classification of TB in
Adults and Children, Am J Respir Crit Care Med
Vol 161, pp. 1376-1395, 2000)
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Rationale for RFQ

• Using universal screening, population prevalence
  of positive TST is lt1, so screening identifies
  more false positives than true positives
• RFQ allows identification of a higher-risk group

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Risk factor screening
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National Recommendations

• Pediatric Tuberculosis Collaborative Group
  recommends risk factor questionnaire (RFQ)
  followed by targeted TB testing
• AAP, ATS, USPSTF oppose universal screening and
  support risk factor screening
• No specific recommendations for content of RFQ or
  optimal age of screening

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Cost-effectiveness analysis

• With limited health care resources, helps
  determine optimal spending
• 50,000 or 100,000 per case of TB prevented
  estimates generally used thresholds for
  cost-effectiveness

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Base-case parameters
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Results

• Preventing one case of TB over the next 20 years
  costs 671,000 if use universal screening instead
  of risk factor screening
• Our results confirm national recommendations to
  discontinue universal screening

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Results-2

• Risk factor screening followed by targeted
  testing costs 524,897 to prevent one case of TB
  compared to no screening

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Why these surprising results?

• In low-prevalence population, many positive TSTs
  are false-positive
• Using the currently recommended RFQ still
  identifies a low-prevalence population
• For screening to be effective, must identify
  higher-prevalence population

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TST positivity by risk group
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(No Transcript)
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TT v. no screening is sensitive to prevalence of
TST-pos among RF-pos

LA Santa Clara (15-18)
Using Froehlich questionnaire in Northern
California pediatric patients Using single
question (foreign birth) in LA or Santa Clara
kindergarteners
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Population parameters meeting 50,000 and
100,000 per TB case averted thresholds, to
select targeted testing (as opposed to no testing)
LA or Santa Clara foreign-born kindergarteners
50,000 per case TB averted
100,000 per case TB averted
Base-case
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TB Surveillance Data, California, 2006
among those with known country of birth (n209)
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Survey results

• 42 (69) of California health jurisdictions
  responded
• 16 (38) of responders required TST prior to
  kindergarten entry
• 51 of 5-year-olds in California live in these 16
  jurisdictions

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Total savings from eliminating universal screening

• Using targeted testing instead of universal
  screening in California would save 1.27 million
• 1.89 additional expected cases of tuberculosis
  over the next 20 years

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Conclusions

• Universal screening of children entering
  kindergarten should be discontinued
• No combination of plausible estimates in
  kindergartners is cost-effective
• Universal screening has outlived its historical
  utility

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Conclusions (2)

• RFQ should be used only where combination of
  circumstances makes it cost-effective
• Guided by local epidemiology takes quite a high
  prevalence of TST-positivity (5) to meet
  threshold
• Single question of foreign birth should be
  considered

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Limitations

• Cost-effectiveness puts a dollar value on
  clinical outcomes, may not reflect clinical goals
• High Number Needed to Screen (NNS), Number Needed
  to Treat (NNT)
• Disregarded potential benefits of case finding
• Few to no TB cases detected even in high
  incidence counties
• Uncertain whether these would have been
  identified at pre-kindergarten check

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Further research

• Cost-effectiveness at different age middle
  school, high school entry
• Will have higher prevalence of latent TB
  infection, higher risk of progression, greater
  risk of spread
• Could possibly have worse compliance, increased
  risk of INH-hepatitis

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Further research (2)

• Development of improved RFQ
• Consider feasibility of single question of place
  of birth
• Much higher PPV than full RFQ but may not be
  politically feasible

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• Thank you

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TT v. no screening not influenced by prevalence
of risk factors
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Froehlich et al.

• 31,926 children KP Northern California
• 37 white, 26 Hispanic, 15 Asian, 12 Black
• 55 0-4, 22 5-9, 17 10-14, 6 15-18

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PPV of RFQ for predicting pos TST