Although "place" has been coined one of the three pillars of epidemiological data, only relatively recently has it garnered significant attention in the public health field, as Geographic Information Systems (GIS) have increasingly become more affordable, accessible, and intuitive. Indeed, the public health community's "place-consciousness" is on the rise as spatial analyses and GIS, now defined as part of the medical and health literature [1–3], are rapidly becoming key components of the public health professional's toolbox [4].

Privacy, an evolving "principle as old as the common law" [5], has been cited as an issue in a variety of public health events, reports, and media releases [6–11]. So much so, in fact, that one sometimes cannot help but wonder if privacy is, indeed, the enemy of public health [12], and whether they could ever peacefully co-exist [13]. A distinction should here be made between the related concepts of privacy, confidentiality, and security within the context of the current discussion. Privacy is attributable to the individual about whom identifiable information pertains, and refers to that individual's right to control such information, thereby freeing the individual from un-invited intrusion and identification. Confidentiality obligates others who have been entrusted with such information to respect the individual's privacy, and is therefore attributable to third parties; a breach of confidentiality violates the privacy of the individual because the individual has had no control over the release of the data. Finally, security refers to tools and methods used to safeguard confidentiality and privacy [14, 15]. This research deals specifically with privacy issues as regulated and defined by legislation and ethical guidelines surrounding consent. From within this context, an individual's privacy is not deemed to have been violated if data shared in the absence of consent cannot be used to identify the individual. Exception clauses generally exist in legislation, allowing authorities to release personally identifiable data under various circumstances – such as where it is deemed to be in the best interest of society or where it is impractical to obtain consent. Examples include Section 60 of the UK's Health and Social Care Act 2001 [16], and Sections 8 and 7 of Canada's Privacy Act [17] and Personal Information Protection and Electronic Documents Act [18], respectively. While an analysis of privacy legislation as it pertains to health data and the concept of "place" is beyond the scope of this paper, suffice it to say that such clauses are often ambiguous and subjective, particularly when combined with vague definitions of "sensitive personal information" and the scale at which geographic data becomes "identifiable". The concept of place, for example, is not explicitly specified as "sensitive personal data" in the UK's Data Protection Act 1988 [19], nor in the generic EU Data Protection Directive of 1995 [20] (though it is explicitly mentioned in various telecommunications directives), but postcodes are specifically mentioned in a 2005 NHS data protection and medical research POSTnote [21]. In Canada's Privacy Act [17], "address" is specifically listed as "personal information", while in the Personal Information Protection and Electronic Documents Act [18], it is not (though implied). Such ambiguities deter the sharing of data, causing organisations and authorities to err on the side of caution and not release identifying information [22], including spatial data.

It is no surprise, therefore, that the increasing popularity of "place" in public health has further exacerbated the public health research-privacy debate. Traditional health-data anonymisation techniques, such as pseudonymisation and aggregation, cannot be applied to spatial data without significantly altering or destroying the spatial relationships under investigation [23–26], and hence the very reason for which they are to be used in the first place. The problem with "place" is that it is most useful at its most precise, granular scale [15, 23]. Yet with increasing spatial precision and accuracy comes a corresponding increase in the risk of identification, and therefore a breach of privacy [15]. This becomes particularly troublesome when the spatial data is linked to health, social or demographic data. The development of methods by which to mitigate these risks continues to be an active area of research, but thus far, proposed solutions have limitations, risks and tradeoffs, and lack guidelines on their appropriate use. Consequently, the acquisition of geographic data tends to be either limited, or at a sub-optimal or unusable scale. Not only do privacy issues impact data acquisition and use for analysis, but also visualisation and dissemination of the results. Researchers have been able to "reverse engineer" maps, for example, to successfully re-identify individuals [27–29].

While the debate between the fields of privacy and public health has raged on for decades [5] despite their interdependence on one another [14], tension continues to rise in concert with the rampant growth of information technology and e-Health. From a health research perspective, both Canada and the UK place strong emphasis on evidence-based public health policies and services [6], yet in both countries, this seems to be hampered by privacy issues. While some argue that this debate is the product of a lack of understanding of the legislation and regulations by the public health community [14, 30, 31], there is little in the way of formal collection and synthesis of the corresponding views and perspectives of those directly involved in public health activities. This paper describes the views and requirements of public health professionals in Canada and the UK on privacy issues and spatial data, as collected through a web-based survey. Given that Canada's health care and public health systems were both largely modeled after those of the UK [6, 32, 33], that each continues to be studied by the other for improvements and lessons learned [6, 34], and that privacy issues for public health have been cited in both, it is expected that survey responses in the two countries will also be similar.

Of 112 invitees in Canada and 75 in the UK, 66 (59%) and 28 (37%) participated in the survey, respectively. Of the Canadian participants, three responded to the French version. The completion proportion for Canada was 91%, and 86% for the UK.

This survey and user-needs assessment on privacy and public health shows a definite requirement by public health professionals – in various fields and positions in both Canada and the UK – for personally identifiable data, including spatial data. The requirement for this spatial data is at its most granular level – latitude and longitude, or exact street address – which necessarily compromises patient privacy. It is not surprising, therefore, that public health professionals perceive privacy to be a significant obstacle to public health practice.

There are those who would argue that this perception is the product of a lack of understanding of the legislation and regulations by the public health community. The results of this research, however, indicate the contrary. Not only did public health professionals in both countries generally rate themselves high on knowledge of privacy legislation and related issues, but those with the highest self-rated scores also tended to rate privacy as more of an obstacle. That these self-ratings of knowledge are not representative of actual knowledge remains possible.

Participants perceived the most critical obstacles to sharing or acquisition of health data with PID to be bureaucracy, followed by legislation.

Bureaucracy surrounding health research in both Canada and the UK generally revolves around data ownership, academic competitiveness, ethics review boards or committees, and in particular, requirements for informed consent, even if they compromise public health, or are not in the best interests of the patients involved [40–42]. Since seeking subject consent with every new hypothesis to be tested or model to be developed is an impossible task, some have suggested that thought be given to "blanket" consent. At the Canadian Institutes for Health Research (CIHI) 2003 workshop on the legal and ethical issues facing the Canadian Lifelong Health Initiative [43], participants spent some time discussing such issues, only to emphasise the importance of the establishment of ethical governance and structure; essentially, more necessary bureaucracy. Interestingly, while the debate continues, a relatively recent survey found that most of the British public did not consider the use of their National Cancer Registry PID for public health research and surveillance to be an invasion of their privacy [30]. While the ethics of blanket consent are not discussed in this study, it is nonetheless offered as a potential solution in light of the requirements of the public health community. This does not, however, address other issues of data ownership and control that contribute to the bureaucratic debate.

While many individuals recognised the importance of privacy legislation, participants generally indicated a concern and, in some cases, first-hand frustration that legislation unduly restricts public health activities, compromising surveillance and research. Many phrases were used by respondents to describe the implications of privacy legislation on public health, including, among others: "increasingly restrictive;" "serious;" "incomplete;" "fuzzy;" "does more harm than good;" "two-edged sword;" "causes challenges;" "delays and restricts access [to data];" " [is a] hindrance to the improvement and efficiency of public health;" "disappointing;" "frustrating;" "difficult to interpret;" "very worrisome;" "disadvantages the public interest;" "not properly understood;" "over-protective;" "limiting;" "hinders knowledge;" and "used as an excuse not to share data." A large proportion of the public health community represented in this sample clearly expressed major concerns with the impact of privacy legislation on their work – both in Canada, and in the UK – in spite of having a good understanding and acceptance of its purpose and necessity. It is also important for legislation to be written in an unambiguous manner that is clearly understood by both public health professionals and the general public [4].

Public health professionals are largely of the opinion that the general public's level of awareness of the impact of restricted access to PID on public health practice is extremely low. Surveys by the Office of the Privacy Commissioner in Canada [44] repeatedly show that the majority of Canadians surveyed (up to 80%) place an extremely high level of importance on strong laws to protect personal information, particularly health information, and that they feel that the level of protection of their personal information has declined over the past ten years. Yet interestingly, only 20% are clearly aware of existing laws, and even fewer (12%) are aware of their rights around the collection, use and disclosure of this information. The "need to raise Canadians' awareness about the current laws in place and what their rights are" [44] must therefore be coupled with the corresponding need to address this from within the context of public health requirements.

Educating the public, therefore, as well as practitioners, data users, policy makers and politicians, was not surprisingly identified by participants as a potential solution. Participants put emphasis on the utilisation of the media to educate and increase awareness, as well as demonstrating the impact of a lack of data, and the benefits of its use when available. Demonstration of the benefits to the individual (e.g. streamlining of the system, not being asked for personal information with every visit to a new clinician, improved dissemination of public health information and intelligence directly to the public) was also offered as a solution, and summed up by one participant in the phrase "seeing is believing". It is worth noting, however, that a number of participants displayed a certain level of pessimism that until a crisis or extreme event occurs, no amount of education or awareness-increasing activities would make a difference.

Public health professionals generally prefer disaggregate, case-level data, but access to this data is an issue. The limitations imposed by privacy on public health have resulted in the development of a variety of techniques for data anonymisation [15, 23, 45]. However, all unavoidably have their issues, risks and limitations, and there is currently no framework to guide public health professionals in their appropriate use and interpretation.

It is clear that privacy is perceived to be a major obstacle and issue for public health – the literature illustrates it, and the current study provides both quantitative and qualitative evidence. Together, these provide a more holistic portrayal of public health community viewpoints, and can be used to educate the public, and as evidence for decision makers to implement changes in policies and legislation. The clash between a requirement for personally identifiable data – including exact, individual location – by public health professionals, and the limitations imposed by privacy and its associated bureaucracy, must be addressed and appropriate solutions developed, particularly given the increasing utilisation of geographic information systems in public health and the imminent completion of comprehensive electronic health systems. Privacy legislation is critical for the protection of this fundamental human right, and to prevent the abuse of personal information, particularly in the health field. However, the legislation must be harmonised with the requirements of public health practice if the health of societies and populations is to be maintained and improved. Since health is not limited by political boundaries, this must be pursued at an international level, and solutions must address these perceptions in the public health community, simplify the bureaucratic process, promote multidisciplinary discussions between legislators, bureaucrats and the public health community, educate communities, and develop and provide public health professionals with toolsets, algorithms and guidelines for using and reporting on disaggregate data. While the results of this study should inform and justify the development of techniques that better anonymise health data with minimal impact on its integrity and frameworks for implementing them, it seems fitting to echo the warning of Curtis et al: "...health and spatial scientists should be proactive and suggest a series of point level spatial confidentiality guidelines before governmental decisions are made which may be reactionary toward the threat of revealing confidential information, thereby imposing draconian limits on research using a GIS [27]."