Arquitectura de Meta-Nivel

Strain typing information can be used to guide public health and clinical action.197 Public health action refers to any additional action that is taken in an attempt to interrupt TB transmission. It includes outbreak investigation and extended contact

93 screening. The public health action that is generated by the TB-STS is initiated through cluster investigations. A cluster investigation is the additional investigation carried out around a cluster of TB cases with indistinguishable strain types. Cluster investigations are initiated based on criteria set out in the TB Strain Typing Cluster Investigation Handbook.197 The criteria, or thresholds, for initiating a cluster investigation relate to the number of cases in the cluster and the characteristics of the cases within the cluster (Box 4). The Handbook was developed as part of the public health component of the TB-STS to guide the public health application of strain typing in England.

Box 4 – Thresholds for the initiation of a cluster investigation

Figure 30 and Figure 31 are from the Handbook197 and show the flow of information and processes that lead to, and constitute a local and national cluster investigation. The criteria and thresholds for investigation are shown in the legend for Figure 30 and Figure 31. Cluster investigations are coordinated by CIs, with local HPUs responsible for local cluster investigations and the national cluster team responsible for national cluster investigations.

The reference laboratories send cluster reports to the CIs on a monthly basis. The London and Birmingham laboratories also send the cluster reports to the relevant

Thresholds/criteria for the initiation of a cluster investigation, as defined in the TB Strain Typing Cluster Investigation Handbook:190

1. Where all the cases in the cluster reside within a single HPU, 5 or more persons within 24 months (2 years), of which 2 occurred in the last 6 months; with TB caused by indistinguishable strains; 2. Where the cases in the cluster reside across more than one HPU within a single region, 10 or more

persons within 24 months (2 years), of which 2 occurred in the last 6 months; with TB caused by indistinguishable strains; and

3. Where the cases in the cluster reside across more than one region, 10 or more persons within 24 months (2 years), of which 2 occurred in the last 6 months; with TB caused by indistinguishable strains.

If the cluster contains any of the risk factors identified as increasing the likelihood of recent transmission, a cluster investigation should be considered when the cluster contains fewer cases than stated in the above thresholds (see the Legend to Figure 30 and Figure 31, page 95, for a list of the risk factors for recent transmission).

94 HPUs. Some HPUs will use the cluster reports sent from the laboratories to inform their decision making. For example, HPUs may use the data to confirm or refute suspected transmission, but many HPUs will wait to receive cluster reports from the CIs as these include recommended actions.

When the CIs receive the cluster reports they carry out a preliminary strain type review. Relevant information about each case is extracted from ETS and, based on the size of the cluster and the characteristics of the cases within the cluster, a judgement is made about whether a cluster should be investigated further and a cluster investigation launched. The summary of the preliminary cluster review and any recommended actions are contained in the cluster report that is then distributed to the relevant HPUs.

From this point, HPUs are responsible for investigating the local clusters identified for further investigation by collecting more information from the clustered patients to try to establish whether there is any evidence for on-going transmission. For national clusters it is the national team that directly contacts TB nurses about their patients. Where there is evidence of on-going transmission, public health interventions may be implemented. Any findings or actions should be reported to the CIs.

95 Figure 30 – A flow chart showing the flow of information and decision making algorithms involved in a local cluster investigation

Legend for Figure 30 and Figure 31

96 Figure 31 – A flow chart showing the flow of information and decision making algorithms involved in a national cluster investigation

97

Human resources

The TB-STS created seven new full-time permanent public health positions and one short-term position: one national Cluster Investigator (CI); four CIs responsible for local and regional clusters; one national strain typing scientist; one national strain typing administrator); and one short-term strain typing administrator for ‘the rest of England’. To cut costs, two of the local/regional CIs were not appointed, leaving the remaining two responsible for clusters in London and the South East, and the rest of England. This did not include the resources allocated for the evaluation. No additional public health positions were created within HPUs or in the NHS.

Cluster investigations

Three different systems have been developed by the CIs to organise and coordinate cluster investigations, based on their access to administrative and technical support and in lieu of the STM.

1. The national CI leads on national cluster investigations from the PHE Centre for Infectious Disease Surveillance and Control in London, collecting information from nurses and HPUs and advising HPUs on further public health and clinical action that may be required. The national CI is supported by a scientist, an administrator and is line managed by the Head of the TB Section.

2. The CI for London and the South East (SE) sits in the regional office in London and sends out cluster reports advising HPUs which clusters should be investigated. The CI provides support to the HPUs, who lead the local investigations and any further public health and clinical action. Regional clusters in London and the SE and some national clusters are coordinated by the CI. The CI for London and the SE is supported by the London Regional Office and line managed by the London Regional Epidemiologist.

3. The CI for the rest of England sits in the North East region and collates the information for cluster reports before sending them to the relevant HPU with

98 recommended actions. Local cluster investigations are led by the local HPU, regional cluster investigations are expected to be led by the HPU with the most cases in that cluster, and any national clusters that are being coordinated by this CI are left to the HPUs to investigate locally with some demographic information about the cases from different HPUs included in the cluster report. Neither local nor regional clusters are coordinated by the CI across the rest of England. The CI for the rest of England had short-term administrative support and is line managed by the TB Lead for the North East.

Training

The aim of the training programme was to enable the implementation of the public health component of the TB-STS by equipping public health and clinical teams to use the strain typing information to inform public health decisions. It involved face- to-face and online resources aimed at those working in HPUs and relevant NHS staff, and was carried out between January 2011 and February 2012. The publication of the Handbook197 and a Q&A sheet215 in December 2010 was the first stage of the training strategy for the TB-STS and provided health protection staff with guidance on how to understand, interpret and use strain typing for TB control. The rest of the training consisted of a workshop at each HPU between January 2011 and February 2012 facilitated by a CI, and a seminar and webcast at the national Health Protection Conference in September 2012.

4.4 Quality assurance