Transcript TB Contact Tracing: organization

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 2012 by the author
ERS School Course on
TB and M/XDR-TB: from clinical management to control and elimination
Session III: Treatment and clinical management
Contact tracing: new principles
Giovanni Sotgiu and Christoph Lange
Bucharest , Friday, 25 May 2012
Contact tracing (CT): outline*
 Definition and epidemiological principles.
 Organization of CT activities:
 Outbreaks in special communities
-
Prisons;
Schools;
Hospitals;
Air travel.
* Source document: Erkens CG, Kamphorst M, Abubakar I, Bothamley GH,
Chemtob D, Haas W, Migliori GB, Rieder HL, Zellweger JP, Lange C.
Tuberculosis contact investigation in low prevalence countries: a European
consensus. Eur Respir J. 2010;36(4):925-49.
TB Contact Tracing: definition
Investigational activity aimed at identifying individuals with TB and LTBI
TB Contact Tracing: aims
TB Control Program
Ultimate goal
STOP transmission
TB Contact Tracing: aims
1) To reduce morbidity and TB-related mortality (target:
secondary cases and latently infected patients).
2) To arrest community/nosocomial transmission (target:
secondary cases and latently infected patients).
2015: 50% reduction in TB prevalence and deaths by 2015
2050: elimination (<1 case SS+ per million population)
TB Contact Tracing: aims
1) a child aged <5 yrs of age is found with TB or infection
without a known source of infection;
2) a person with TB likely due to recent infection (primary
tuberculosis) is found without a known source of
infection;
3) a cluster of persons with TST or IGRA conversion is found
in a high-risk institution.
TB Contact Tracing: principles
 Characteristics of the contacts (e.g. duration of exposure, immune
system status, etc.).
 Characteristics of the index case (e.g. infectiousness, etc.).
Contact
Index case
Contact
Secondary cases through CT:
1% of identified contacts
(Jereb J et al. Int J Tuberc Lung Dis 2003; 7.)
Contact
Contact
Contact
Contact
TB Contact Tracing: principles
Identifying routes of transmission
Traditional contact tracing
Index case
Traditional contact tracing
Molecular typing
Spoligotyping – Complement to RFLP &/or MIRU-VNTR
IS 6110 RFLP
MIRU-VNTR
Gold standard
Up to 24 loci in genome
Molecular epidemiology
Molecular
technique
Advantages
Disadvantages
IS 6110 RFLP
Highly disciminatory
Time-consuming, technically demanding,
interlab-comparison, low-copy n. isolates
MIRU-VNTR
Simple, rapid, inter-lab
comparison
Less disciminatory – depending on n. loci
analysed
Spoligotyping
Low-cost, simple,
reproducibility
Least discriminatory, overestimates epilinks
Molecular epidemiology
 Identify unexpected outbreaks – unexpected links between patients
Cross-jurisdictional outbreaks
Identify weakness in TB Control Program (quality evaluation)
TB Contact Tracing: principles
 The greatest risk of developing TB after a median incubation period
of 6 wks.
 Exponential decline of the TB risk during the first 7 yrs (60% who
develops TB: within 1 yr).
 After 7 yrs persistent low risk of developing TB (about 1 per 1,000
person-yrs).
Early incidence is determined by the age
at which infection is acquired
2%
Primary school
30-40%
Infant
TB Contact Tracing: principles
The lifetime risk of TB=
risk during the first years (age-related) and cumulative incidence during
the low-incidence period (life expectancy-related)
TB Contact Tracing: principles
 Lifetime risk of a child (beyond the highest risk period) is
cumulatively 10% (from Comstock).
 Age-weighted average risk in the UK is 12% (from Vynnycky) vs.
10-20% in Germany (from Horsburgh).
 Two-year risk of TB in IGRA+ is 15% in Germany (from Diel).
TB Contact Tracing: principles
The extent of CT depends on:
 degree of contagiousness of the index/secondary cases,
 period of infectiousness of the index/secondary cases,
 location(s) of transmission,
 risk of the infected contacts to develop TB,
 no. of infected individuals.
TB Contact Tracing: infectiousness
Infectiousness with pulmonary TB, but:
-TB mediastinal or hilar lymphadenopathy;
-Pleural effusion and other extra-pulmonary forms;
-TB/HIV co-infection
CT only after the confirmation of a concomitant pulmonary TB
TB Contact Tracing: infectiousness
Ability to aerosolise bacilli and n. of aerosolised bacilli
Talking
Coughing
Sneezing
Singing
TB Contact Tracing: infectiousness
Ability to aerosolise bacilli and n. of aerosolised bacilli
Cavitary lesions
TB Contact Tracing: infectiousness
Assessment of the following parameters :
-Pulmonary TB;
-Production of sputum
-Results of sputum smear examination;
-Results of sputum culture;
-Cavitations;
-Coughing.
TB Contact Tracing: infectiousness
Period of contagiousness:
 Diagnostic delay (pt- and/or healthcare system-related).
 Start of anti-TB treatment (2 wks?; DR strains?; 
nosocomial transmission & negative-pressure isolation
room; household management).
 Initiation of cough or of any other TB symptom.
TB Contact Tracing: infectiousness
Period of contagiousness:
1)
Pulmonary cases SS+ deemed potentially infectious for the period the patient is known to
have been coughing (initially to a maximum of 3 months). The presence of radiologically
identifiable cavitations increases the assumed degree of infectiousness.
2)
Pulmonary cases with culture+ pulmonary TB and 2 SS- may be considered potentially
infectious for 1 month before the date of TB diagnosis, where the presence of cough or a
cavity increases the assumed degree of infectiousness.
3)
A person with drug susceptible pulmonary TB should be considered potentially infectious
until the person has completed 2 wks of appropriate treatment in the absence of any
suspicion or proof of MDR-TB and has improvement from symptoms.
TB Contact Tracing: infectiousness
Evaluation of the potential location
Outdoor
Indoor
 ☺Sunlight
 ☻ Room size
 ☺Ventilation
 ☺Ventilation
 ☻Talking distance
 ☻Household density
TB Contact Tracing: infectiousness
Susceptibility of the contacts
TB Contact Tracing: infectiousness
Susceptibility of the contacts:
risk of TB after infection in children
The probability of disease in children and in adults occur in the first 6–
12 months following primary infection.
The longer remaining life expectancy adds to a cumulatively larger
lifetime risk in children
 children <5 yrs of age are a main target for CT
TB Contact Tracing:
diagnostic algorithm
Immunological diagnosis (TST, IGRA)
Microbiological diagnosis (SS, NAAT)
Medical History
Physical examination
Chest radiography
TB Contact Tracing:
diagnostic algorithm
Medical history
TB Contact Tracing: organization
Risk assessment
Infectiousness of the index case;
Duration of exposure to the index case;
Risk of TB in infected contacts.
TB Contact Tracing: organization
Risk assessment: 2 strategies
“Risk group” approach: I&E of high priority* contacts
with a prolonged exposure, followed by I&E according to the
individual risk of progression to TB;
‘‘Stone in-the-pond” approach: I&E of high priority
contacts with a prolonged exposure, followed by I&E to
medium-priority contacts according to the transmission
pattern among high priority contacts and identification of
those with a higher risk of progression to TB.
*Includes those exposed to a high bacillary load for a short period.
TB Contact Tracing: organization
Risk assessment
Interview of the index case
on his/her social network
Degree of exposure =
intensity and duration
Highest risk of
developing TB
TB Contact Tracing: organization
Risk assessment
TB Contact Tracing: organization
Risk assessment
TB Contact Tracing: organization
TB Contact Tracing: organization
TB Contact Tracing: organization
Chest radiography is indicated at the same time as the
initial TST or IGRA if the contact:
has symptoms suggestive of TB;
is HIV+ or has another immunosuppressive disorder or
exposed to immuno-suppressive medications;
is <5 yrs of age;
TST reaction size is > 5 mm or the initial IGRA is positive.
TB Contact Tracing: organization
TB Contact Tracing: organization
Window period: time period between acquisition of TB
infection and the point in time when an immunologic
response becomes measurable.
In all high-priority contacts, or in case of an initially negative
TST or IGRA in a high priority contact, the evaluation should
be performed or repeated when ≥8 wks (1–2 wks beyond the
median window period) have passed since the last relevant
exposure to the index case.
TB Contact Tracing: organization
In children <5 yrs prophylactic treatment may be stopped if
the repeat TST remains negative unless <6 months.
Contacts with HIV infection or other severe
immunosuppressive disorders re-evaluated after completion
of 2 months of preventive therapy.
TB Contact Tracing: organization
Expansion of CT?
Risk group approach: other vulnerable contacts
Concentric-circles approach: evidence of recent transmission
among the high priority contacts.
Contacts with TST or IGRA conversions.
Young children with a positive TST or IGRA.
Contact with TB.
The observed prevalence of infection is higher than the
Expected prevalence.
TB Contact Tracing: organization
Expansion of CT?
Evaluation of medium-priority contacts after the first
screening of the high-priority contacts (examined once after
the window period).
No evaluation of low-priority contacts unless there has been
transmission among medium-priority contacts (examined
once after the window period).
TB Contact Tracing: M&E
Aims
1) assess whether all persons with an increased risk of
having become infected have been informed and/or
screened;
2) assess whether other exposed groups need to be targeted
for CT;
3) Evaluate the organisation, performance and effectiveness
of procedures;
4) provide data for evidence based guidelines on CT.
TB Contact Tracing: M&E
TB Contact Tracing: communication
Absence of any ‘‘medical emergencies’’ for CT vs. urgency due to
anxiety of potential contacts and of their families (increased by media).
It is crucial to provide correct information and reassurance to the
contacts and authorities ASAP.
To reduce the negative impact of misleading and incorrect messages,
health authorities should prepare a press release.
TB Contact Tracing: outbreak
Occurrence of ≥ 2 TB cases, outside the household setting,
with an epidemiological and/or molecular link occurring
within 1 yr.
Outbreak control committee: a respiratory physician, public
health specialists, a microbiologist and administrative
members.
 communication, coordination and epidemiological analysis
TB Contact Tracing: outbreak
DNA fingerprint technology enables the identification of
molecular clusters (laboratory cross-contamination).
Confirmation with information on epidemiological and social
relationships.
TB Contact Tracing: outbreak
Congregate settings
Large groups of individuals are confined to areas with
limited air circulation.
Need of large CT depends on:
-infectiousness of the source case,
-degree of overcrowding (shelters for the homeless),
-susceptibility of the population.
TB Contact Tracing: outbreak
Prisons
Prevention:
Early detection (screening of detainees upon incarceration),
infection control measures, adequate treatment of susceptibleand MDR-TB cases, case-holding after release from prison.
Higher risk due to IVDUs, alcohol abusers, homeless,
mentally ill, foreign-born persons and former prisoners.
TB Contact Tracing: outbreak
Schools
Lower threshold for widening the investigation.
Transmission can affect a substantial number of contacts.
Communication of prevention and control procedures to
staff, parents and the general public to prevent anxiety and
media misleading info.
TB Contact Tracing: outbreak
Hospitals
Causes: delays in diagnosis and failures in infection
control.
Focus on risk of exposure of immunocompromised patients
and hospital staff (including lab staff).
Infection control plan and coordination of CT activities.
TB Contact Tracing: outbreak
Air travel
Exposure to SS+ pt on a flight of ≥8 hrs within the
preceding 3 months.
I&E of passengers sitting in the same row and the two rows
ahead and behind the source case.
TB Contact Tracing:
critical features
Lack of evidence on the cost-effectiveness of the
interventions.
Lack of accurate tools predicting the risk of developing TB.
Effective preventive therapy.
Adherence to preventive therapy
Molecular investigation.