Management at the Scene of Overt Releases

Overview

An overt release assumes that the release of a biological agent is clearly identifiable: there may be a prior warning, or the release may be apparent, either due to the use of an explosive device, or because a suspicious substance is obviously visible.

It may or may not be possible to reliably identify the nature of an overtly released substance. It may be a hazardous biological or chemical agent, or may simply be a harmless substance released as a hoax or confused with a genuine deliberate release. Guidance for the investigation and management of outbreaks and incidents of unusual illness can be found here

For infections caused by inhalation, the greatest risk to health is during primary aerosolisation when infectious particles are initially airborne. Once particles have settled, there may be a continuing risk of infection from cutaneous and hand to mouth contact or secondary aerosolisation, but this tends to be lower.

Defining an exposed zone

The release of a biological agent will create an exposed zone: an area and time period in which the agent has been dispersed, and which poses a risk of infection.

None of the organisms likely to be used in deliberate releases have a reliable test to indicate whether people have been exposed. Initial targeting of prophylactic treatment therefore relies on an assessment of the extent of the exposed zone. Defining the exposed zone following an overt release is the responsibility of security services. The area will be cordoned off until appropriate environmental decontamination has ensured that there is no further risk of infection.

The location and size of the exposed zone will depend on the site of release, the mechanism of dispersal of the agent, and local geographical and meteorological factors. It will also depend on the properties of the particles used to disperse the agent: for example with anthrax, fine particles may carry further following primary

aerosolisation, take longer to settle, and pose a risk of secondary aerosolisation if they are subsequently disturbed. The duration of the exposed zone will depend on the time of release and the survival of the agent used.

Protection of frontline workers

This includes all emergency staff involved in management at the scene of a release, as well as those involved in treating patients.

Personal Protective Equipment

The exposed zone presents a high risk of infection. Any personnel entering this zone should wear a biologically-resistant suit with outer gloves and boots (for example a CR1, PRPS or gas-tight suit) and a correctly fitting high-efficacy particulate respirator of FFP3 standard AT ALL TIMES.

Healthcare workers will not normally be asked to enter this zone, but may be called into it to treat casualties, for example if an explosive device has accompanied the release of a biological agent. In this case the appropriate protective clothing and equipment should be worn.

Other protective measures

Depending on the agent, consideration may also be given to offering prophylactic treatments to frontline workers involved at the scene of a deliberate release.

Procedure for handling exposed persons

All individuals who have been present in the exposed zone need to be identified. Some of them will still be at the scene of the incident when emergency services arrive. This group should be moved through a decontamination process and then to a place of safety for medical assessment and prophylactic treatment if necessary. Others may have left the scene before emergency services arrive and will need to be identified later - they may approach GPs and Emergency Departments after details of the incident have been made public. Procedures need to ensure that all of these individuals are decontaminated, receive appropriate prophylactic treatment, and have their details collected for follow-up.

Decontamination

Decontamination facilities should be established at the scene. Exposed persons should first remove their clothing and place inside labelled double plastic bags. They should then be instructed to shower thoroughly, including hair washing, using soap and water, before being given clean clothes and proceeding for medical assessment.

Handling contaminated clothing

The risk of re-aerosolisation of agents from clothing is low, but frontline workers should wear appropriate protective clothing and equipment and observe Standard Universal Precautions - gloves and gowns and hand washing - and avoid agitation when handling contaminated items. Once removed, contaminated clothing should be placed inside double plastic bags, which should be sealed and labelled and stored until exposure to an organism has been ruled out.

Depending on the organism, subsequent decontamination of clothing may vary as shown below.

Decontamination of clothing

Medical assessment

Following decontamination, exposed persons should proceed to a place of safety: a clinical area outside the exposed zone but within the cordon established at the scene. Here they can be assessed by healthcare staff. They can be given appropriate prophylactic treatment if necessary, and their personal details can be collected in case follow-up is required.

Healthcare staff who attend exposed persons after decontamination has been completed do not need to take any special precautions. Even if individuals have been infected with agents that are capable of person-to-person transmission, they will not be contagious until symptoms arise.

Providing information

Information sheets have been prepared for distribution in the event of an incident.

Surveillance and case finding

Following an overt deliberate release, cases of disease may occur in people not initially thought to have been exposed. Clinicians and hospitals should therefore actively look out for presentations of illnesses due to deliberate release, so that if they arise, early treatment can be started, patients can be isolated if necessary, and epidemiological details can be followed-up.

As epidemiological data from cases and results from environmental testing become available, the definition of the exposed zone may be refined and extended. In this event, further exposed persons will need to be identified, contaminated clothing dealt with, and appropriate prophylactic treatment issued.

Last reviewed: 29 December 2011