Use of Network Analysis During
a Tuberculosis Investigation
Outbreak Investigation Section
Surveillance and Epidemiology Branch
Division of Tuberculosis Elimination
National Center for HIV, STD, and TB Prevention
Centers for Disease Control and Prevention
Atlanta, 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
M. tuberculosis Transmission
• Infectiousness
• Exposure duration
• Room size
• Air exchange
TB patient
Contact
Exposure…. Infection…. Disease
Exposed
contacts
Latent
TB
infection
Tuberculin
Skin
Test
Active
TB
disease
Concentric Circle Approach
Household
Casual Contacts
Close Contacts
Leisure
TB
PATIENT
Work
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)
50% TST+
A
50% TST+
B
50% TST+
50% TST+
C
D
Patient C has greater importance, but patient-specific
TST-positive rates miss this importance
No Shortage of Data
Contacts
Data
• Name, address, DOB
• Sex, ethnicity
• Places
• TST status
• Type of contact
• Strength of contact
• All the case variables
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
Jail
Restaurant
Fever &
Cough
ED Visits
1
Ju
l0
01
Ju
n
01
M
ay
1
A
pr
0
1
ar
0
M
01
Fe
b
01
Ja
n
00
D
ec
N
ov
00
Diagnosis
of TB
Contact Investigation:
Index Case-Patient
Identified Tested
TST+ (5 mm) RR (95%CI)
Household
11 10
Friend
76
63
33 (52%)
3.4 (1.5,7.8)
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)
294
251
106 (42%)
Jail
Total
10 (100%)
6.4 (2.9,14.3)
Case-Patients by Date of
Diagnosis (N=35) Nov 02
8
Culture confirmed
Clinical Case
CDC invited
4
Index
2
2001
2002
Nov
Sep
Oct
Aug
Jul
Jun
May
Apr
Mar
Jan
Feb
Dec
Nov
Sep
Oct
Aug
Jul
0
Jun
Case
6
Contact Investigations
Total Identified
Evaluated
TST  5mm
Initiated treatment
Female
Age <5
5-14
15-24
25
Black
N (%)
1,039
860 (83)
179 (21)
135 (75)
474 (53)
45 ( 5)
171 (20)
169 (19)
507 (57)
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
45
43
37
20
32
36
29
2
18
3
22
21
12
33
19
1
16
34
9
13
8
4
7
14
10
30
35
5
6
11
38
39
17
15
25
What Does the Entire
Network Look Like?
Entire Network
How Are Infected Contacts
Related to the Cases?
Case-patients and LTBI
Which Contacts Should We
Pursue for More Information?
Network Core
How Do You Prioritize?
Contacts Needing Evaluation
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, MD
Epidemic Intelligence Service Officer
Division of TB Elimination
CDC
Local and State TB Control Authorities
Valdis E. Krebs
InFlow Software™
http://www.orgnet.com