Contact tracing

Contact tracing is the activity of identifying the relevant contacts of a person with an infectious disease (index patient) and ensuring that they are aware of their exposure and implement necessary measures. The term relevant reflects the specificity of the actual disease in terms of person, place and time.

Contact – case definition

Contact tracing is defined as the identification and follow-up of persons who may have come into contact with an infected person. Contact tracing is an important part of the epidemiologic investigation and active surveillance. (WHO)

Persons can be labelled as contacts if they comply with the definition of the contact; they spent sufficient time and in physical proximity with the index case that has stage of disease suitable for transmission.

Why to do contact tracing?

The purpose of contact tracing is to detect the first symptoms of the disease in contacts, monitor them and treat if the disease is confirmed. Secondary prevention is one of the purposes and is focused on preventing the development of the disease in exposed persons. Tertiary prevention is the prevention of severe outcomes and sequelae in exposed persons that developed the disease. The public health purpose is to limit transmission and contain the outbreak.

When is contact tracing done?

In general, contact tracing is carried out when the transmission route is direct contact, casual or sexual.

Pre-test contact tracing is done when high patient concerns exist, and the time to wait for laboratory results may be detrimental for the exposed persons. Post-test contact tracing is done after a confirmed diagnosis in the index case. This approach may reduce social and personal (emotional and mental) damage to the possible contacts. Principles of contact tracing

Principles of contact tracing are the same for all diseases, but they differ in the length of follow-up and frequency of monitoring sessions.

Contact listing and follow up

All persons considered to have had exposure as by the definition of the contact and taking into consideration different risk categories should be listed as contacts, using predefined (standardised) contact listing form.

How far into case history should we investigate?

The periods for potential contact tracing differ among diseases and should be taken as a general guide only:

- Chancroid – 2 weeks before ulcer appeared or since arrival in endemic area
- Chlamydia – 6 months
- Donovanosis – Weeks to months, according to sexual history
- Ebola viral disease – 21 days (similarly Lassa fever and Marburg HF)
- Gonorrhoea – 2 months
- Hepatitis A – 50 days from onset of symptoms
- Hepatitis B – 6 months prior to onset of acute symptoms
- Hepatitis C – 6 months prior to onset of acute symptoms; if asymptomatic according to risk history
- HIV – Start with recent sexual or needle-sharing partners; outer limit is onset of risk behaviour or last known negative HIV test result if known
- Lymphogranuloma venereum – 1 month or since arrival in endemic area
- Mycoplasma genitalium – Unknown, insufficient data on some infections, partner notification is likely to be beneficial and is recommended in these cases and should be guided by the sexual history
- Syphilis
-- Primary syphilis – 3 months plus duration of symptoms
-- Secondary syphilis – 6 months plus duration of symptoms
-- Early latent syphilis – 12 months
- Trichomoniasis – Unknown, insufficient data on some infections, partner notification is likely to be beneficial and is recommended in these cases and should be guided by the sexual history
- Tuberculosis – 3 months prior to diagnosis, unless there is evidence of protracted symptomatic illness prior to this date.

References:

• Australasian Contact Tracing Manual, published by the: Australasian Society for HIV Medicine (ASHM), 2010, http://ctm.ashm.org.au/Default.asp?PublicationID=6&ParentSectionID=P6&SectionID=733
• Contact tracing during an outbreak of Ebola virus disease, September 2014, Disease Surveillance and Response Programme Area, Disease Prevention and Control Cluster, World Health Organization, Regional Office for Africa, Brazzaville, 2014 ISBN: 978 929 023 2575 (NLM classification: WC 534)