Surveillance for Health Protection in England and Wales: An analysis of NHS Direct syndromic data

Abstract

Disease surveillance is the collection and analysis health data to provide information for action and to inform decisions relating to public health policy. Surveillance systems in the UK typically rely on data about diagnoses made by clinicians, or laboratory confirmations of specific disease pathogens. In recent years there has been a growth in syndromic surveillance systems that collect and analyse pre-diagnostic information in real-time in order to provide early warning of rises in disease, and estimate the health status of the community. The research question of this thesis is: “What is contribution of NHS Direct data to health protection surveillance in England and Wales?” NHS Direct is a nurse-led health helpline (telehealth system) available to the entire population of England and Wales. Health protection surveillance is the surveillance of infectious diseases and environmental hazards that may pose a threat to public health. NHS Direct data are suitable for surveillance purposes because they are broadly representative of the health seeking behaviour of those aged below 65 years in England and Wales, and are available nationally on a daily basis. The seasonality of syndromes indicative of infection is largely determined by viral rather than bacterial diseases. Half the seasonal variation in respiratory syndromes reported to NHS Direct is estimated to be due to RSV and influenza. Rotavirus and norovirus are estimated to be the most important enteric pathogens determining the seasonality of diarrhoea and vomiting calls. The surveillance system has detected seasonal trends and acute rises in these syndromes at both regional and national level. However, retrospective analyses and operational results have not, in any consistent way, demonstrated value for local outbreak detection. The main added value of these data for health protection is for influenza surveillance. Numerical threshold values for calls about the ‘cold/flu’ and fever syndromes consistently provide 1-2 weeks advance warning of national rises in influenza A and B. Spatio-temporal analysis of fever calls about school aged children also provided a unique description of the spatial evolution of a national influenza outbreak, with utility for local and national surveillance. Additionally, self-sampling by NHS Direct callers is a feasible method of providing laboratory diagnoses, and enhancing community surveillance schemes. NHS Direct syndromic data have also been used for providing early warning of regional and national rises in viral gastroenteritis, heatstroke, hay fever. When interviewed, the system’s users (those who receive surveillance alerts) reported additional benefits of the system were for validating other hard and soft intelligence sources, managing winter pressures on the NHS, surveillance response and reassurance during major incidents, and handling the media. It is recommended that the HPA explore further the use of the data for prospective geographical surveillance of influenza, norovirus and heatstroke. Also that the HPA and NHS Direct attempt to extract data about multiple symptoms linked to a single NHS Direct caller. Finally, other countries should consider surveillance of telehealth data if there is a perceived need to develop real-time monitoring of common syndromes (i.e. there are recognised shortfalls in existing primary care surveillance).