Does Screening and Contact Tracing for Tuberculosis Make Sense?

Size: px

Start display at page:

Download "Does Screening and Contact Tracing for Tuberculosis Make Sense?"

Laurence Wade
6 years ago
Views:

1 Des Screening and Cntact Tracing fr Tuberculsis Make Sense? Rencntre Genevise de Pneumlgie HUG, mercredi 29 avril 2009 Hans L Rieder Incident cases f tuberculsis emerge unpredictably frm the ppulatin prevalently infected with M tuberculsis Ppulatin including persns with and withut infectin with M tuberculsis 1

2 Where des M. tuberculsis spread? The Cmmunity Infectin Rati Indicatr Ppulatin (denminatr) Infected (numeratr) Prevalence (p) 1-prevalence (q) Cmmunity Cntacts p/q p/q cmm / p/q cntacts 0.19 (CI: ) Example: Shaw J B, Wynn-Williams N. Am Rev Tuberc 1954;69: Methd: Madic G, et. Lancet 2002;345:416-9 The cmmunity infectin rati with M tuberculsis 0.6 Cmmunity infectin rati Spreads in cmmunity Spreads in husehld 0.0 Bedfrdshire UK Leeds UK British Clumbia Suth India US Suth Lima, Peru Madic G, et. Lancet 2002;345:

3 Fractin f cases / infected Sensitivity f Direct Sputum Smear Examinatin in Identifying Pulmnary Tuberculsis and Transmitters Smear-neg Culture-ps Smear-ps Culture-ps Cases f pulmnary tuberculsis Infected cntacts < 15 yr Fractin due t smear-neg cases Fractin due t smear-ps cases Calculated frm data frm: Grzybwski S, et al. Bull Int Unin Tuberc Lung Dis 1975;50: Prevalence f Infectin Amng Childhd Cntacts <5yr by Characteristic f Bacterilgically Cnfirmed Surce /1,012 Per cent infected Cugh + Sputum + 71/286 Cugh + Sputum - 24/244 Cugh - Sputum - Hertzberg G. Acta Tuberc Scand 1957;38(S-1):

4 Risk f Infectin Given Expsure: Largely Exgenus Factrs Particles Vlume x Expsure time Particles: Vlume: Expsure time: Prductin f infectius drplet nuclei Vlume f air and ventilatin Time f inhaling air with drplet nuclei Risk f Infectin Amng Cntacts as a Functin f the Prximity f Cntact 4

5 Which cntacts are at particular risk f disease given infectin? Denminatrs and numeratrs Whse cntacts shuld be cnsidered? All pulmnary cases? likely inefficient All smear-psitive cases: Prblem: what is smear-psitive? Which cntacts are at risk f infectin? Critical: duratin f expsure Age and immunsuppressin are the principle cnsideratins The Stne-in-the-Pnd Principle 102 / 2,748 = 4.0% 5 / 40 =12.5% 14 / 3,646 = 0.4% Simplified after data frm: Veen J. Tuber Lung Dis 1992;73:73-6 5

6 The Dutch Supermarket Apprach Brgen K, et. Eur Respir J 2008;32: Number f cases / cntacts Secndary Cases f Tuberculsis Amng Cntacts, by Prximity and Smear Grade in Index Case, Finland, Cntacts 286 casual 67 clse 134 Index cases casual 69 clse Cntacts 65 4 secndary cases Liipp KK. Am Rev Respir Dis 1993;148:

7 The Litmus Test: Case Incidence Given a Test Result Incidence Case Rate Amng Husehld Cntacts f Smear- Psitive Tuberculsis, by Intitial Tuberculin and IGRA Test, Gambia Incidence per 100,000 p-yr Mx: ES: Mx- ES- Mantux Elispt %! ES+ Mx- ES- Mx+ Mx+ ES- Mx- ES+ Mx+ ES+ Mx+ r ES+ Hill PC, et al. PLS One 2008;3(1): e1379. di: /jurnal.pne A simplified view f a prblem: Tuberculin skin test versus IGRAs Bth tests measure the wrng thing, but IGRAs d it mre specifically An immunlgic respnse t mycbacterial antigens acquired in the past des nt equate currently live bacilli ready t cause disease (BCG!) 7

8 The chice between IGRA types I dn t want t be bthered with cmplexities It s the lymphcytes, stupid Smart Nt s smart Simple Nt available Available Nt s simple Available Nt a chance A ratinal strategy that will never be heeded? Examine first nly husehld cntacts f direct (nt BAL) sputum smear-psitive cases, aged less than sme cut-ff age Calculate prevalence f infected If critical prevalence threshld exceeded nly, examine ther clse cntacts Examine cntacts f all pulmnary cases aged <5yrs 8

9 Hw t determine a cut-ff f critical prevalence? Depends n the predictive value f a psitive test result (test-type dependent prer fr tuberculin test with increasing age) UK chse 10 per cent Cmpile yur wn data and then revise cut-ff based n data Break all rules nly with children under age f 5 years as lng as they live in the husehld verkill might be justified A cld epidemilgic view f reality? Cntact tracing and testing is an inefficient rllback and cntainment strategy: the damage has been dne and cannt be identified efficiently Preventive therapy is a nice theretical cncept, but the tests available d nt identify the right peple Regard cntact tracing and preventive therapy strictly as an individual measure t cntain the wrst damage: children under age f 5 years living in the same husehld as a ptential surce f transmissin Accept the deficiencies f peratin damage cntrl and live with it, yu cannt cmpensate it justifiably by extending cntact tracing 9

Chapter 6: Impact Indicators

Chapter 6: Impact Indicators Overview Chapter 6: Impact Indicatrs The best measure f the lng-term impact f all HIV preventin activities is the HIV incidence rate, namely the number f new cases f HIV infectin per year divided by the