REFLECTIONS ON PHASE SPECIFIC APPROACHES TO THE EPIDEMIOLOGY AND PREVENTION OF STDS

Discussions in Rome revealed several, rather striking patterns. Firstly, while a considerable volume of data is available in most areas, much more empirical data are required to describe phases of epidemics as they are influenced by social, economic, political, legal, and epidemiological contextual factors. Particularly, behavioural data and contextual data were unavailable in most countries. In addition, there is a clear paucity of longitudinal or temporal trend data that are essential in studying phase related concepts. Longitudinal data on behaviours and societal factors were unavailable in most cases; however, longitudinal morbidity data were also unavailable in many cases. It appears that research and surveillance activities predominantly focus on STDs themselves and to a limited extent on individual behaviours associated with STD acquisition. Moreover, most research and surveillance activity tends to be conducted within local boundaries, without much attention to sexual links that relate local sexual networks to each other. It may be important to consider the establishment of surveillance systems that include monitoring of contextual parameters and social determinants at regional and global levels.^{10, 14} Not surprising is the variation in data availability between resource poor and resource rich settings. However, even in resource rich settings data are not being collected in standardised ways that permit comparative longitudinal analyses across societies, across pathogens, and through time. This latter type of analysis would be most helpful to the further development of phase specific approaches.

Secondly, measurement and classification of epidemic phases is highly variable. Not surprisingly, there is inconsistent interpretation of levels of STD prevalence and incidence, inflection points in the course of epidemics, and epidemic phases.¹¹ Clearly, STD prevalence and incidence levels that are considered hyperendemic in low prevalence societies may be considered low prevalence plateaus in high prevalence societies. Clarification of phase versus morbidity level concepts and development of methodologies that allow measurement and monitoring of phase related parameters would be helpful in this regard.

Easy to use, rapid measurements of network related parameters constitute another important need. Standardised measures of the extent and nature of sex work within populations and the size and nature of the interactions among core groups, bridge populations, and the general population would help both research efforts and programmatic activities.^{10, 11}

Thirdly, the phase specific model, in its current form, is particularly applicable in resource rich environments, even though it is implicitly used in many resource poor settings. Whether future elaborations of the model may increase its applicability in resource poor environments remains to be seen. In its current form the phase specific STD epidemiology model is a unilinear evolutionary model. Consideration of variations of epidemic trajectory around the postulated ideal typical course may render the model more applicable in resource poor settings. It appears that in resource poor settings the programmatic activities postulated by the model are not realised at the scale assured in the model. As a result, the dynamic tension between STD spread and the programmatic forces that limit such spread, which is central to the phase specific model, and which is clearly observable in resource rich settings, is absent in resource poor settings.

RECOMMENDATIONS AND FUTURE DIRECTIONS

A number of recommendations emerged as a result of discussions in Rome, some of which have been mentioned above. At the theoretical level, there was broad agreement that the phase specific model has important theoretical and practical implications and that future work should focus on continuous refinement of phase related concepts through theoretical and empirical research. At the empirical level, there was agreement that a phase specific approach to the collection of epidemiological data was helpful and this framework should be utilised. In this context it was clear that the lack of behavioural and contextual data limited both our understanding of the evolution of STD epidemics and the ability of STD programmes to develop interventions for the prevention of STDs. The recommendation is that behavioural, contextual, and STD data be collected longitudinally, suggesting a major investment and reorientation in STD surveillance systems.¹⁴

In the methodological domain recommendations included the development of phase relevant measures, and standardised measures to assess and monitor the size of core groups and core bridge general population interactions.^{10, 11} It was also recommended that such measures be utilised in empirical work globally to allow comparative analyses of STD epidemiology across countries. Another methodological recommendation involved the development of summary measures describing sexual networks to be incorporated in mathematical models of STD transmission dynamics.

In addition, the group suggested that empirical work with sex worker populations, their clients, and other high risk groups adopt quantitative approaches, which may permit better assessment of the size of such groups and the extent of sexual mixing across groups.

Recommendations for STD prevention programmes varied somewhat between resource poor and resource rich settings. However, the recommendation that the phase of the epidemic be considered in programme planning and in targeting programmatic interventions was applicable to all environments. Similarly, the suggestion that programmatic attention be focused on sex workers was applicable to all environments.

Finally, several suggestions were made for the formation of special interest groups and there was broad agreement that a similar meeting should be held in 3–5 years' time. In this context, a meeting focusing on the development of summary measures of sexual networks to be incorporated in mathematical models of STD transmission dynamics is scheduled to take place in April 2002, and a work group focusing on sex workers has been established and will start functioning shortly.

STD epidemiology and prevention science has expanded greatly in the past two decades. The increased interaction among programme planners, mathematical modellers, network analysts, social scientists, and epidemiologists promises even greater advances in the future. Following up on the suggestions included in this supplement through multidisciplinary efforts may bring us closer to innovative, science based, and effective prevention programmes.