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Contact
Evaluation
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International Standards 18, 19
Contact Evaluation
Objectives: At the end of this presentation
participants will be able to:
 Describe how Mycobacterium tuberculosis (M.tb)
is transmitted
 Evaluate the risk of transmission based on the
clinical extent of disease and diagnostic tests
 Identify and evaluate contacts who are at
increased risk for acquisition of infection
 Determine who among contacts is at greatest risk
should infection occur
 Make decisions concerning the treatment of latent
tuberculosis infection
ISTC TB Training Modules 2009
Contact Evaluation
Overview:
 Value (yield) of contact
evaluation
 Transmission of M.tb
 Clinical factors influencing
transmission
 Evaluating contacts and
determining priorities
 Vulnerable contacts
 Treatment of infected
contacts
International Standards 18, 19
ISTC TB Training Modules 2009
Standard 18: Contact Evaluation
(1 of 2)
All providers of care for patients with TB should
ensure that persons who are in close contact with
patients who have infectious TB are evaluated and
managed in line with international recommendations.
The determination of priorities for contact investigation
is based on the likelihood that a contact:
1) Has undiagnosed TB
2) Is at high risk of developing TB if infected
3) Is at risk of having severe TB if the disease
develops
4) Is at high risk of having been infected by the index
case.
ISTC TB Training Modules 2009
Standard 18: Contact Evaluation
(2 of 2)
The highest priority contacts
for evaluation are:
 Persons with symptoms
suggestive of tuberculosis
 Children aged <5 years
 Contacts with known or
suspected
immunocompromise,
particularly HIV infection
 Contacts of patients with
MDR/XDR tuberculosis
 Other close contacts are
a lower priority group
ISTC TB Training Modules 2009
Standards for Public Health
ISTC TB Training Modules 2009
Yield of Contact Evaluations: All Active TB
 On average, 4.4 household
contacts were investigated per
index case
 4.5% of evaluated household
contacts will have active TB
 Therefore, investigation of
approximately 5 households
yields one active TB case
pooled estimate
% of Contacts with Active TB (with or without positive bacteriology): Systematic Review.
Graph compares results of individual studies in low- and middle-income countries.
Pooled average of all studies indicated by arrow.
Morrison J et al. Lancet ID 2008
ISTC TB Training Modules 2009
Yield of Contact Evaluations: LTBI
LTBI among household contacts
 Nearly one-half of the household
contacts evaluated had LTBI
indicated by a positive tuberculin skin
test, but a negative evaluation for
active TB.
pooled estimate
% Contacts with LTBI: Systematic Review.
Graph compares results of individual studies in low- and middle-income countries.
Pooled average of all studies marked by arrow.
Morrison J et al. Lancet ID 2008
ISTC TB Training Modules 2009
Yield: Active TB and LTBI by Age
TB1
LTBI2
< 5 years
8.5
30.4
5 –14
6.0
47.9
All < 15
7.0
40.4
6.5
64.6
Children
Adults
1 = % of examined contacts with clinical and confirmed TB
2 = % of examined contacts with latent TB infection
Morrison J et al. Lancet ID 2008
ISTC TB Training Modules 2009
Transmission
of M.tb
ISTC TB Training Modules 2009
Transmission of M.tb
Droplet nuclei
CASE
CONTACT
Environment
 Site of TB
 Cough
 Bacillary load
 Treatment
ISTC TB Training Modules 2009
 Ventilation
 Filtration
 U.V. light
 Closeness and
duration of contact
 Immune status
 Previous infection
Generation of Droplet Nuclei
 One cough produces
500 droplets
 The average TB
patient generates
75,000 droplets per
day before therapy
 This falls to 25
infectious droplets per
day within two weeks
of effective therapy
ISTC TB Training Modules 2009
Fate of M.tb Aerosols
 Large droplets settle
to the ground quickly
100 µm
 Droplets < 100 m
fall <1 meter before
evaporating to
1-10 mm size
Evaporation
 Smaller droplets form
“droplet nuclei” of 1-5 µm
diameter and can be inhaled
and deposited in the distal airspaces
 Droplet nuclei remain airborne indefinitely
ISTC TB Training Modules 2009
5 µm
Effect of Therapy on M.tb
Log cfu
Effective multi-drug therapy reduces bacillary load
0
2
4
6
8
10
12
14
Weeks
ISTC TB Training Modules 2009
16
18
20
22
24
Assessing Infectiousness
 High degree of infectiousness
• Sputum smear-positive pulmonary TB
• Symptomatic with cough
• Cavitation on chest radiograph (correlates with
positive smear)
 Lesser degree of infectiousness
• Sputum smear-negative, culture positive
pulmonary TB
• Minimal if any cough
• Lesser radiographic extent of disease
• Extrapulmonary TB
ISTC TB Training Modules 2009
Indices of Infectiousness
Tuberculin Reactors (%)
among household contacts
Radiographic extent of disease
Minimal
16.1
Moderately advanced
28.3
Far advanced (cavitary)
61.5
Bacteriologic status
Smear –, culture –
14.3
Smear –, culture +
21.4
Smear +, culture +
44.3
Mean 8-hour overnight cough count
< 12
27.5
12-48
31.8
> 48
43.9
Source-Case Variables
Loudon RG. ARRD 1969;99:109-11
ISTC TB Training Modules 2009
Prevalence of Infection in Contacts
Source Case status
Smear + Smear – Smear –
General
Age (yrs)
Culture ? Culture + Culture – Population
0-4
29.1%
6.0%
6.5%
0.7%
5-9
35.9
12.4
6.2
0.9
10-14
39.5
14.1
19.1
2.2
15-19
47.0
18.1
18.1
4.2
20-29
51.5
32.9
43.4
10.5
30-39
59.2
52.2
46.2
21.3
40+
61.1
50.3
47.9
38.5
Grzybowski S. BIUAT 1975;60:90
ISTC TB Training Modules 2009
Evaluating
Contacts &
Determining
Priorities
ISTC TB Training Modules 2009
Decisions in Contact Evaluation
 Deciding to initiate a contact evaluation
 Investigating the index case and sites of
transmission
 Identifying contacts and assigning
priorities
 Evaluation of contacts
 Treatment for contacts with latent
tuberculosis infection
ISTC TB Training Modules 2009
Circles of Contacts
Index case
Uninfected, 2
Uninfected, 10
Infected, 3
Infected, 5
Household Contacts
Average 4 – 5/case
Out-of-Household
Contacts
(Work, school, social)
Unknown number
ISTC TB Training Modules 2009
Identification of Contacts
 Interview newly diagnosed TB patients to
identify contacts
 Focus on those in same household but don’t
neglect out-of-household contacts
 Tailor interview to patient’s circumstances
(homeless, congregate living facility, etc.)
 Determine the circumstances of exposure, and
attempt to quantify the closeness and duration
 Determine if there are other persons within the
group of contacts who have symptoms
associated with TB
ISTC TB Training Modules 2009
Levels of Exposure
Closeness and duration of exposure
• Grading exposure settings
1.Size of a car
2.Size of a bedroom
3.Size of a house
4.Larger than a house
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Levels of Exposure
Estimating critical exposure duration
• Thresholds are highly variable
• Exposure duration threshold should be
determined by index case
characteristics, settings, contact risk
factors
ISTC TB Training Modules 2009
Priorities in Contact Evaluation
At greatest risk of acquiring infection
• Close contacts of smear positive index cases
• Persons with HIV infection (?)
• Highly exposed persons
At greatest risk of active TB
• Children < 5 years of age
• Persons with HIV infection
• Persons with other immunocompromising
conditions or therapies
ISTC TB Training Modules 2009
Priorities in Contact Evaluation
Contacts to
MDR/XDR cases
• Prioritize active
case-finding to
reduce further
transmission of
drug-resistant
disease
ISTC TB Training Modules 2009
Initial Assessments of Contacts
Assessment depends on local circumstances,
resources, and policies.
 Minimal evaluation: Question contacts about
symptoms and evaluate if symptoms are present
 Tuberculin skin test followed by chest
radiographs for all positives (either > 5 mm or
> 10mm, depending on local policies)
 Chest radiographs for all children < 5 years of
age
 Sputum examinations for all symptomatic
contacts and all with radiographic abnormalities
ISTC TB Training Modules 2009
Isoniazid Preventive Therapy: Rationale
 Risk of active tuberculosis is greatest
soon after infection occurs
 Contacts of infectious cases are likely to
have been infected recently
 Treatment of those found to have a
positive tuberculin skin test will reduce the
likelihood of active tuberculosis
ISTC TB Training Modules 2009
Isoniazid Preventive Therapy: Evaluation
 Evaluate all potential LTBI treatment
candidates for active TB
 Identify those who have been treated
previously
 Identify those with contraindications to
treatment for LTBI (prior allergic reactions,
severe unstable liver disease)
 Identify co-morbid conditions and other
medications being used
ISTC TB Training Modules 2009
Isoniazid Preventive Therapy: Priorities
 Children < 5 years
of age
 Persons with
HIV infection
 Persons with other
immunocompromising
conditions
 Close contacts of highly infectious index case
 Persons with other conditions that increase
risk (example: silicosis)
ISTC TB Training Modules 2009
ISTC Standard 19: IPT
Children <5 years of age and persons of any
age with HIV infection who are close
contacts of an infectious index patient and
who, after careful evaluation, do not have
active tuberculosis, should be treated for
presumed latent tuberculosis infection with
isoniazid
ISTC TB Training Modules 2009
Contact Evaluation
Summary:
 Between 4 and 5 % of household
contacts of new cases will be found to
have active TB and 50% will have LTBI
 The likelihood of transmission relates
directly to the bacillary burden of the
index case
 Environmental factors also play an
important role
ISTC TB Training Modules 2009
Contact Evaluation
Summary (continued):
 Priorities for evaluation include children
< 5 years of age, persons with HIV
infection, contacts of MDR/XDR cases,
and highly exposed contacts
 Treatment of LTBI may be indicated for
high priority contacts
ISTC TB Training Modules 2009
Summary: ISTC Standards Covered*
Standard 18:
 All providers of care for patients with TB should
ensure that persons (especially if symptoms
suggestive of TB, children under 5 years of age,
persons with HIV infection, and contacts to
MDR/XDR) who are in close contact with patients
who have infectious TB are evaluated and managed
in line with international recommendations.
 The determination of priorities for contact
investigation is based on the likelihood that a
contact: 1) has undiagnosed TB; 2) is at high risk of
developing TB if infected; 3) is at risk of having
severe TB if the disease develops; and 4) is at high
risk of having been infected by the index case.
*Abbreviated version
ISTC TB Training Modules 2009
Summary: ISTC Standards Covered
Standard 19:
 Children < 5 years of age and persons of any
age with HIV infection who are close contacts of
an infectious index patient and who, after careful
evaluation, do not have active tuberculosis,
should be treated for presumed latent
tuberculosis infection with isoniazid
ISTC TB Training Modules 2009
Alternate Slides
ISTC TB Training Modules 2009
Purpose of ISTC
ISTC TB Training Modules 2009
ISTC: Key Points
 21 Standards (revised/renumbered in 2009)
 Differ from existing guidelines: standards
present what should be done, whereas,
guidelines describe how the action is to be
accomplished
 Evidence-based, living document
 Developed in tandem with Patients’ Charter
for Tuberculosis Care
 Handbook for using the International
Standards for Tuberculosis Care
ISTC TB Training Modules 2009
ISTC: Key Points
 Audience: all health care practitioners,
public and private
 Scope: diagnosis, treatment, and public
health responsibilities; intended to
complement local and national guidelines
 Rationale: sound tuberculosis control
requires the effective engagement of all
providers in providing high quality care and
in collaborating with TB control programs
ISTC TB Training Modules 2009
Questions
ISTC TB Training Modules 2009
Contact Evaluation
1. A 23 year-old school teacher has recently been
diagnosed with active pulmonary TB. She is
concerned about the risk of transmitting disease
to the children she teaches in a small, poorlyventilated classroom. Aspects of her clinical
presentation that would suggest a higher
degree of infectious risk include all of the
following except:
A. Sputum smear positive for M. tuberculosis
B. Significant cough symptoms
C. Cavitary-disease on chest film
D. Extrapulmonary cervical lymphadenitis
ISTC TB Training Modules 2009
Contact Evaluation
2. A 42 year-old man has been diagnosed with
smear-positive pulmonary TB. He works five
days per week as an accountant in a small
office with two other co-workers and lives in an
apartment building with his wife and son. Other
activities include a 2-hour weekly football game
with his teammates outdoors. (Continued)
ISTC TB Training Modules 2009
Contact Evaluation
2. (Cont.) In regards to planning a contact evaluation for
this case, lowest priority for assessment would be:
A. Assessment of the clinical factors that influence
infectious risk, such as the presence and duration
of cough symptoms
B. Gathering information regarding age, health status
(especially risk for HIV), and presence of TB
symptoms in any close contacts
C. Evaluation of his outdoor football teammates as
contacts
D. Evaluation of the size and ventilation of the office
space, and the amount of contact time between coworkers and the patient
ISTC TB Training Modules 2009
Contact Evaluation
3. Contacts to an infectious pulmonary case of TB
found to have latent TB infection (LTBI) who
have the highest risks for progression to active
TB disease once infected include:
A. Children <5 years of age
B. Spouses due to the extended duration of exposure
C. Persons with HIV infection
D. Both A and C
ISTC TB Training Modules 2009