Research Article: Control of Trachoma in Australia: A Model Based Evaluation of Current Interventions

Date Published: April 10, 2015

Publisher: Public Library of Science

Author(s): Andrew J. Shattock, Manoj Gambhir, Hugh R. Taylor, Carleigh S. Cowling, John M. Kaldor, David P. Wilson, Jeremiah M. Ngondi. http://doi.org/10.1371/journal.pntd.0003474

Abstract: BackgroundAustralia is the only high-income country in which endemic trachoma persists. In response, the Australian Government has recently invested heavily towards the nationwide control of the disease.Methodology/Principal FindingsA novel simulation model was developed to reflect the trachoma epidemic in Australian Aboriginal communities. The model, which incorporates demographic, migration, mixing, and biological heterogeneities, was used to evaluate recent intervention measures against counterfactual past scenarios, and also to assess the potential impact of a series of hypothesized future intervention measures relative to the current national strategy and intensity. The model simulations indicate that, under the current intervention strategy and intensity, the likelihood of controlling trachoma to less than 5% prevalence among 5–9 year-old children in hyperendemic communities by 2020 is 31% (19%–43%). By shifting intervention priorities such that large increases in the facial cleanliness of children are observed, this likelihood of controlling trachoma in hyperendemic communities is increased to 64% (53%–76%). The most effective intervention strategy incorporated large-scale antibiotic distribution programs whilst attaining ambitious yet feasible screening, treatment, facial cleanliness and housing construction targets. Accordingly, the estimated likelihood of controlling trachoma in these communities is increased to 86% (76%–95%).Conclusions/SignificanceMaintaining the current intervention strategy and intensity is unlikely to be sufficient to control trachoma across Australia by 2020. However, by shifting the intervention strategy and increasing intensity, the likelihood of controlling trachoma nationwide can be significantly increased.

Partial Text: Australia is the only high-income country in which trachoma, the worldwide leading cause of preventable blindness [1], remains endemic [2]. In remote Aboriginal communities deemed to be at-risk of trachoma, an estimated 4% of adults suffer severely impaired vision or blindness [3] due to many years of repeated re-infection with the bacterium Chlamydia trachomatis—the infectious agent from which trachoma disease develops [4]. In 2009, the Australian government pledged AUS$16 million over an initial four-year period towards the national goal of controlling trachoma by 2020 [3]. That is, to reduce the prevalence of trachomatous inflammation follicular (TF) to less than 5% amongst 5–9 year-old children within a community. This target closely aligns with the Global Elimination of Trachoma by 2020 (GET 2020) initiative [5] developed by the World Health Organisation (WHO). The Australian trachoma intervention effort combines annual surveillance activities with a Surgery, Antibiotics, Facial cleanliness and Environmental improvement (SAFE) control policy recommended by the WHO [3,6]. This four-component policy incorporates treatment for those with clinically detected disease and long-term solutions for reducing infection incidence and disease prevalence [7]. The WHO offers recommendations for the frequency and intensity of the screening and treatment programs integrated into the SAFE policy [8]; however, the Australian intervention effort involves a greater intensity of screening and treatment due to larger resource availability compared to other trachoma-endemic countries. Despite this, the prevalence of trachoma remains high in many Aboriginal communities [3] whilst several developing countries prepare to announce the national control or eradication of the disease [9].

The model developed for this study simulates a population of Aboriginal persons within a remote Australian region. Each individual represented in the model is a member of an at-risk community encompassed by the region, and is also a resident of a household within a community (Fig 1A). The temporary migration of individuals (and potentially other members of their household) is simulated based on rates of movement between communities [19].

Model-based evaluations of the interventions implemented between 2007 and 2011 suggest that disease prevalence has generally been reduced through trachoma intervention efforts. However, the scale of impact of the past intervention measures was found to vary between regions. The greatest reductions were observed in the predominantly hyperendemic regions, where trachoma prevalence among 5–9 year old children was estimated to have been 23.5% (mean from 1,000 simulations, with range 18.5%–30.7%) in 2011 in the absence of interventions compared with 14.3% (10.5%–18.5%) with interventions; in the predominantly mesoendemic region, trachoma prevalence was estimated to have reduced from 14.8% (10.3%–19.7%) to 5.8% (3.2%–8.0%) due to intervention efforts (Fig 2). However, the impact of intervention measures in the predominantly hypoendemic region is more modest: disease prevalence in 2011 was estimated to have reduced from 5.1% (2.2%–8.9%) to 4.3% (2.3%–6.5%) (Fig 2). This occurs despite a comparable, if not stronger, screening and treatment effort being observed in the hypoendemic region. Indeed, the mean 5–9 year old screening coverage from 2007 to 2011 in the predominantly mesoendemic and predominantly hypoendemic regions are 70.5% and 78.9%, respectively. The corresponding values for treatment coverage were 87.6% and 86.1%, respectively. A sensitivity analysis of model input parameters (see S1 File) suggests that this finding may be influenced by a higher baseline prevalence of child facial cleanliness in the predominantly hypoendemic region.

Australia is the only high-income country to have endemic trachoma. Whilst being a signatory to the WHO’s GET 2020 initiative, the Australian government has responded to the health issue in recent years with large investment. However, as several developing countries with histories of trachoma prepare to announce the national control or eradication of the disease [9], high prevalence levels of trachoma are still observed in remote Australian Aboriginal communities. Since 2006, Australia has implemented national surveillance activities to collect age-segregated community-level data describing the timing, frequency and intensity of screening and treatment programs as well as disease prevalence, facial cleanliness prevalence, and more recently environmental conditions that may affect trachoma incidence and persistence [3,23,27]. Increases in community screening and treatment, along with recorded increases in facial cleanliness among children has correlated with declines in trachoma prevalence in Australia.

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http://doi.org/10.1371/journal.pntd.0003474

 

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