Staff have learned what it is like to work intensively at that speed under public and political scrutiny, and it has been useful training for future events, such as pandemic flu

At the end of November, the Health Protection Agency faced its largest single incident yet. polonium-210 had been identified as the poison that killed Alexander Litvinenko and traces of the radiation were found in hotels, offices, aeroplanes and restaurants across London. A meeting was called of the government's emergency planning body the Cabinet Office Briefing Rooms (COBR), and the HPA was asked to secure public health and maintain public confidence.

It was essential to communicate quickly to the public that alpha radiation was not a threat to public health when it was in a container and that it only represented a radiation hazard if it was taken into the body - by breathing it in, taking it into the mouth, or through a wound. Failure to get this message across could have resulted in unnecessary alarm and a loss of public confidence.

Although poisoning using internal radiation was an unprecedented event, the HPA had both a generic emergency plan and specific ones involving radiation. Our radiation division had experience of working with polonium and alpha radiation and were able to test for it, both in clinical specimens and the environment. These factors enabled us to respond, but the unusual nature of the event required us to learn new approaches and modify our plan.

Goals and responses
Our objectives were to protect individuals and the wider public and to maintain public confidence. Our response was based on a risk assessment, which was continuously updated. Initially, the risk assessment was based on expert knowledge of alpha radiation, then refined using modelling to assess risk in different scenarios. This was then validated using the monitoring and clinical data as it became available.

In the early stages, because of the uncertainty about many of the details of the incident and the implications, we took a precautionary approach - hence we contacted staff and called for customers in specific locations to contact NHS Direct, which passed the details to us. Some of the callers were referred to a specialist clinic, but in most cases we called them and took details, in case we needed to recall them for follow-up, and to include them on a long-term database. At that stage, we also placed a high priority on following up Mr Litvinenko's family and the hospital staff.

Thereafter, there was a pattern - as soon as an area of concern was identified by the police, we monitored all public areas within that site, assessed the risk, and followed up staff and visitors to those venues. As a result, we have identified a number of people with a very small long term risk to their health, but for most people, even if they had been in contact with radiation, we have found no short or long-term risk.

This has been an intense programme of work which was anything but straightforward, with new issues arising at various times. For example, we had to switch monitoring teams when urgent priorities arose, such as the arrival of planes at short notice and being asked to deploy teams. We were able to call on other agencies to support this work, and at one time we were co-ordinating 19 monitoring teams at various sites, with others covering other shifts so we could work on a 24/7 basis.

Huge follow-up effort
As well as the monitoring programme, the other huge volume of work has been following up people, assessing them, testing their urine samples, and advising them of results. The scale-up of what is usually a research process into mass screening was a major exercise. Similarly contacting large numbers of people required several teams. Many people were genuinely anxious. Those given the all-clear showed palpable relief to our staff, and those with levels which gave them measurable, albeit very small, long-term risk needed detailed individual discussions.

Two other major strands of work were international and communications. The situation by its nature was international, with considerable overseas interest. Many of the visitors to the hotels and restaurants were from other countries, and this has required considerable liaison with embassies and public health bodies across the world. On communications we have held two press conferences, given many interviews, put out regular updates and responded to hundreds of media enquires. Our aim was to give honest and authoritative information and advice.

The situation is not over, but it has tested us and shown to me that the HPA can respond. The professionalism of our staff has been obvious; many people have been outstanding in their performance and it has been encouraging to see people from all over the HPA working as one team. They have learned what it is like to work intensively at that speed under public and political scrutiny, and it has been useful training for future events, such as pandemic flu.

It has also shown the difference from an exercise, and particularly the need to be flexible, and to have resilience, sustainability and business continuity over a period of time; infections have not gone away because of polonium. It has pinpointed some training needs, and a requirement for succession planning. We will carry out a formal debrief, which we will share widely and which will be invaluable for our future work.

Dr Pat Troop is chief executive of the Health Protection Agency.