Use of Network Analysis During a Tuberculosis Investigation

Outbreak Investigation SectionSurveillance and Epidemiology Branch

Division of Tuberculosis EliminationNational Center for HIV, STD, and TB Prevention

Centers for Disease Control and PreventionAtlanta, GA

April 21, 2003

TB Facts

• M. tuberculosis (M.Tb) airborne transmission

• Latent TB infection (LTBI) detected by tuberculin skin test (TST)

• 10 to 15 million LTBI

• 10% lifetime risk of progression to active TB

TB patient Contact

M. tuberculosis Transmission

• Infectiousness

• Exposure duration

• Room size

• Air exchange

Exposedcontacts

Latent TB

infectionActive

TBdisease

Exposure…. Infection…. Disease

TuberculinSkinTest

Concentric Circle ApproachHousehold

Leisure Work TB PATIENT

Close Contacts

Casual Contacts

Multiple Contact Investigations

The Concentric Circle Paradigm Assumes…

• Cases know their contacts

• Cases will reveal their contacts

• Casual contacts are less important

• Interconnections among contacts of contacts are unimportant

Each Contact Investigation Yields an Individual Transmission Unit

TB patient “A” identifies 2 contacts

Contact evaluated and found to be tuberculin skin test (TST) positive

Contact evaluated and found to be tuberculin skin test (TST) negative

County’s Contact Data from Multiple TB Cases (A–D)

Patient C has greater importance, but patient-specific TST-positive rates miss this importance

A

50% TST+

B

50% TST+

D

50% TST+

C

50% TST+

Contacts Data

• Name, address, DOB

• Sex, ethnicity

• Places

• TST status

• Type of contact

• Strength of contact

• All the case variables

No Shortage of Data

Outbreak

Objectives

• Identify case-patients and contacts

• Establish epidemiologic links among case-patients and contacts

• Make recommendations to control the outbreak

Methods

• Case-patients

• Contacts

• Data entered in ACCESS® database*

• InFlow™ 3.0 network analysis software*

*Use of trade names and commercial sources is for identification only and does not imply endorsement by the U.S. Department of Health and Human Services

Index Case-Patient

ED Visits

ED Visits

Diagnosisof TB

Restaurant

Fever &Cough

Jail

Contact Investigation: Index Case-Patient

Identified Tested TST+ (5 mm) RR (95%CI)

Household 11 10 10 (100%) 6.4 (2.9,14.3)

Friend 76 63 33 (52%) 3.4 (1.5,7.8)

Jail 125 108 54 (50%) 3.2 (1.4,7.3) Work/School 40 32 5 (16%) Referent

Hospital 42 38 4 (11%) 0.7 (0.2,2.3)

Total 294 251 106 (42%)

Case-Patients by Date of Diagnosis (N=35) Nov 02

Culture confirmed Clinical Case

Index

2001 2002

CDC invited

Contact Investigations N (%)

Total Identified 1,039Evaluated 860 (83)TST 5mm 179 (21)Initiated treatment 135 (75)

Female 474 (53)Age <5 45 ( 5)

5-14 171 (20) 15-24 169 (19) 25 507 (57)

Black 390 (48)

Network Visualization

Network Key

Nodes

TB cases

TST(+) contacts

TST(-) contacts

TST status unknown

Links

Close contact

Casual contact

Are All TB Cases Associated?

Case-Patients

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What Does the Entire Network Look Like?

Entire Network

How Are Infected Contacts Related to the Cases?

Case-patients and LTBI

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Which Contacts Should We Pursue for More Information?

Network Core

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How Do You Prioritize?

Contacts Needing Evaluation

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Conclusions

Conclusion: EPI Data

• Delayed diagnosis generated a large community outbreak in a low incidence area

• All case-patients were linked to index case-patient

• High TST reaction rate around the index case-patient

Conclusion: Network-Informed Approach

• Proved feasible in a low incidence setting

• Required no new data; based on routine contact investigations

• Facilitated discussions between state and county TB controllers

Acknowledgments

McKenzie Andre, MDEpidemic Intelligence Service OfficerDivision of TB EliminationCDC

Local and State TB Control Authorities

Valdis E. KrebsInFlow Software™http://www.orgnet.com