Laboratory Procedures

Risk assessment

Lassa, Ebola, Marburg and CCHF are hazard group 4 pathogens, and should thus be covered by existing risk assessments for handling such organisms in diagnostic laboratories. These facilities are available at either HPA Colindale or HPA Porton, where all specimens must be sent for diagnosis.

It is recognised that in the event of a covert deliberate release specimens from the first unsuspected cases might be examined in Regional laboratories before the diagnosis is known. If VHF is not suspected, routine investigation will inevitably be done in local laboratories. If VHF is suspected, then the level of exposure of the patient should be categorised based on the risk categories shown below.

Categorising risk for VHF

Risk Category	Description
Minimum Risk	Febrile patients who have been in contact with a known or suspected source of VHF but in whom the onset of illness was definitely more than 21 days after their last contact with any potential source of infection
Moderate Risk	Febrile patients who: were adjacent to an exposed zone in the 21 days prior to onset of an illness which has similar signs and symptoms as VHF Or Lived in or stayed in a house for more than 4 hours where there were ill, feverish persons known or strongly suspected to have a VHF
High Risk	Febrile patients who: Have been in the exposed zone Or Took part in nursing or caring for ill feverish patients who had or suspected to have VHF Or Had contact with the body fluids, tissue or the dead body of such patients Or Were previously categorised as moderate risk, but who have developed organ failure and / or haemorrhage

For minimum risk patients, key investigations such as malaria film can be done in a Containment Level 2 laboratory with eye and face protection. For those in the moderate risk group, investigations such as malaria can be undertaken in a Class 1 microbiological safety cabinet in Containment Level 3 laboratory. If VHF cannot be ruled out, any further investigation should be done in a Containment Level 4 (CL4) laboratory.

All investigations for patients in high-risk category should be undertaken in a CL4 laboratory currently located at either HPA Colindale or HPA Porton. If the capacity of CL4 laboratories for routine investigations (not direct viral investigations) is exhausted, then after appropriate risk assessment and discussion with HPA Colindale or HPA Porton automated blood counting machines and chemistry analysers may have to be used as long as they are designated for this purpose and work in a closed system (see ACDP, HMSO 1996 for further details).

In exceptional circumstances such as deliberate release the numbers of cases may quickly exhaust the available facilities. In these situations patients will have to be nursed in cohort isolation in a designated ward and patient support laboratory investigations carried out using closed system blood analysers. If specimen handling for these purposes could produce an aerosol, e.g. in blood cross matching, then these procedures must be carried out in a category 3 laboratory inside a Class I or Class III microbiological safety cabinet. In no circumstances should any procedures that may lead to propagation of the viruses be carried out, these specimens must be referred to the reference laboratories.

Receipt of samples

Samples should be labelled as High Risk by the submitting staff and discussed with the receiving laboratory. Samples should be handled according to local protocols for such samples. Chain-of-evidence documentation should accompany specimens. In larger incidents, this would only be required for several of the initial cases.

Isolation and identification

These viruses can be cultured in vero E6 cells but this should only be attempted in a Containment Level 4 laboratory. RT-PCR tests have been described for all four viruses and this is the first line diagnostic test. Identification of virus is on the basis of specific amplification and sequencing. The laboratory must be warned in advance that samples are being submitted.

Confirmation

Serological confirmation is possible by IF or ELISA but antibodies may not be detectable when the patient first presents. Acute and convalescent sera should be sent to the Reference Laboratory for testing. The laboratory must be warned in advance that sera are being submitted.

Reference laboratories

Samples should be packed and labelled according to current regulations for Hazard group 4 pathogens. The procedures outlined in transport of clinical specimens must be observed, and the Reference Laboratory should be notified when samples are despatched. All specimens, including sera, should be sent to:

Dr David Brown or Dr Robin Gopal
HPA Colindale
Viral Zoonosis Unit
Enteric, Respiratory and Neurological Virus Laboratory
61 Colindale Avenue
London NW9 5HT

Tel: (+44) 0208 327 3117

or 020 8200 4400 (24 hour)

Click here for further information on ERNVL and referral of specimens and samples

and

Dr Tim Brooks
HPA Porton
Special Pathogens Reference Unit Porton Down
Salisbury
Wiltshire SP4 0JG

Tel: (+44) 01980 612224

or 01980 612100 (24 hour)

Click here for more information on SPRU and referral of specimens and samples

Waste disposal

Waste should be disposed of according to local procedures for Containment Level 4 Laboratory.

Last reviewed: 11 May 2011