Trachoma is one of the top ten most common blinding diseases  and the leading cause of preventable blindness worldwide . One person is left with severe sight loss every four minutes due to the damage caused by trachoma infection; four people are blinded by the disease every hour . Endemic in more than 50 countries worldwide , trachoma has been classified by the World Health Organisation (WHO) as one of 17 neglected tropical diseases (NTDs). Its cause is infection of the eye surface by the bacteria Chlamydia trachomatis . Recurrent infection leads to painful in-turning of the eyelashes (trichiasis), which, if left untreated, scratch and subsequently scar the eyeball, resulting in the cornea becoming opaque and, ultimately, blindness [1,4]. The bacteria are readily transmitted through infected discharge – therefore the disease can be spread through shared items such as towels, as well as by eye-seeking flies . People that live in crowded conditions and with poor sanitation are particularly susceptible to the spread of trachoma . This means that the disease burden, in terms of human suffering and reduced quality of life for those infected, their families and wider communities, is shouldered by some of the world’s poorest populations .
In addition to prevalence and impact on quality of life, the burden of a disease can also be measured in terms of monetary losses, referred to as economic burden of a disease. Estimating the economic burden of different diseases is useful when resources and funding for health interventions are limited, as it allows the cost-effectiveness of proposed control strategies to be evaluated in monetary terms.
To understand the economic burden of NTDs, we searched the key sources of health-related publications, including PubMed, the WHO and Cochrane websites, using a combination of disease-related and economy-related search terms. Disease-related search terms included all of the 17 NTDs, as defined by the WHO , and economy-related search terms such as ‘burden’, ‘cost’ and ‘employment’. Diseases with inexpensive treatments that affect the largest populations were prioritised. In total, we found 282 articles reporting on the economic burden of NTDs in developing countries, which we then divided by disease area. The 12 resulting articles on trachoma were used as basis for this review.
A number of studies presented estimates of the occurrence of trachoma at various scales - individual countries, continents and worldwide. One study estimated that, globally, trachoma is the cause of blindness in 1.3 million people and trichiasis in a further 8.2 million . It is thought that 110 million people live in areas where trachoma is endemic , including Pakistan, Senegal, Nepal and Fiji , and are therefore at risk of contracting the disease. Within these endemic areas, 4.6 million people already suffer with late-stage-trachoma and will require surgery to prevent blindness. Worryingly, a further 210 million people currently live in areas where trachoma is suspected, but not confirmed .
Some of these studies converted the disease prevalence into health burden, measured in disability-adjusted or handicap-adjusted life years (DALYs, which are a measure of healthy life-years lost due to disability and mortality; or HALYs, which are a measure of years lived in a handicapped state and mortality); others used the prevalence data to calculate the economic burden of trachoma. The global estimate of the health burden of trachoma was 80 million HALYs ; the estimated economic burden was $2.9 billion . The geographic distribution of trachoma infection is very patchy, with 80% of the global burden concentrated in only 14 countries , and 97% of the burden of Latin America and the Caribbean found in Brazil alone . Perhaps unsurprisingly, NTDs have been shown to have particularly high prevalence in conflict and post-conflict countries, for example trachoma in Sudan, Mali and Niger .
Generally, estimates of the burden of trachoma vary considerably between different reports , most likely due to the fact that prevalence figures are not consistent between studies; and there seems to be no standard conversion method to generate estimates of human or economic burden. Accurate estimates of disease burden are therefore difficult to generate. However, even if not completely accurate, estimating the disease burden is undoubtedly useful, as it allows assessment of the cost-effectiveness of disease control or elimination strategies and provides decision makers with additional information to help prioritise healthcare interventions.
An innovative strategy which targets trachoma from both a medical and a socioeconomic angle , ‘The SAFE Strategy’ (surgery and antibiotics, promoting facial cleanliness and environmental change), is endorsed by the World Health Foundation . The potential of SAFE has been demonstrated in Morocco, where the prevalence of trachoma has been reduced by 75% since its implementation in the late 1990s, and complete elimination of the disease has been achieved in some provinces . This is by no means an isolated case - a further 9 countries, including Ghana, Vietnam and The Gambia, have reported meeting their targets towards the elimination of blinding trachoma . The total cost of implementing the SAFE strategy in all remaining known endemic countries is estimated to be $430-$748 million , which is less than a third of the estimated overall economic burden of trachoma.
An alliance of interested parties, led by the WHO, has set the target of the global elimination of trachoma for 2020 (GET2020). Pfizer, a major pharmaceutical company, has committed to help. They have donated over 225 million doses of azithromycin (an antibiotic) to date , allowing the treatment to cure or prevent trachoma for 48.8 million people . However a 2012 review suggested that lack of funding may still be a barrier to achieving the GET2020 goal . Interestingly, the authors of this review estimated that diverting just 10% of the funding allocated to the treatment of the ‘Big Three’ diseases (tuberculosis, HIV and malaria) to NTDs would allow the achievement of the GET2020 goal .
As the occurrence of NTDs is so often linked to the living conditions in poor rural communities, it is likely that any healthcare interventions introduced will contribute to the decrease of more than one disease simultaneously. For example, it has been suggested that the framework set up to provide treatment for onchocerciasis (another NTD, which also causes blindness) can also be used to distribute azithromycin, or any other drug . Therefore, if NTDs are considered individually, the effectiveness calculated for interventions may well be underestimated. In many cases, it will be more appropriate to consider the reduction of the burden of multiple diseases when calculating the cost-effectiveness of a single intervention strategy.
Overall, it is clear that NTDs, such as trachoma, cause immense human suffering and remain a serious impediment to poverty reduction and overall socioeconomic development . Our research into trachoma, as well as onchocerciasis and cysticercosis [16, 17], has shown that these NTDs each impose a significant economic as well as health burden on affected communities. Although there has been much progress in tackling this global problem by introducing control measures, such as SAFE, continued strategic investment is necessary if the targets for the reduction and eradication of these diseases are to be met.
By Katie Hamilton and Julia Bardos, working pro bono on behalf of Costello Medical Consulting, with a wider team at Costello Medical Consulting
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