Overview
Trachoma is the leading infectious cause of blindness worldwide. It is caused by an obligate intracellular bacterium called Chlamydia trachomatis. The infection is transmitted by direct or indirect transfer of eye and nose discharges of infected people, particularly young children who harbour the principal reservoir of infection. These discharges can be spread by particular species of flies.
Epidemiology and clinical features
In areas where trachoma is endemic, active (inflammatory) trachoma is common among preschool-aged children, with prevalence rates which can be as high as 60–90%. Infection becomes less frequent and shorter in duration with increasing age. Infection is usually acquired when living in close proximity to others with active disease, and the family is the main setting for transmission. An individual’s immune system can clear a single episode of infection, but in endemic communities re-acquisition of the organism occurs frequently.
After years of repeated infection, the inside of the eyelid can become so severely scarred (trachomatous conjunctival scarring) that it turns inwards and causes the eyelashes to rub against the eyeball (trachomatous trichiasis), resulting in constant pain and light intolerance. This and other alterations of the eye can lead to scarring of the cornea. Left untreated, this condition leads to the formation of irreversible opacities, with resulting visual impairment or blindness. The age at which this occurs depends on several factors including local transmission intensity. In very highly endemic communities it can occur in childhood, though onset of visual impairment between the ages of 30 and 40 years is more typical.
Visual impairment or blindness results in a worsening of the life experience of affected individuals and their families, who are normally already amongst the poorest of the poor. Women are blinded up to 4 times as often as men, probably due to their close contact with infected children and their resulting greater frequency of infection episodes.
Environmental factors associated with more intense transmission of C. trachomatis include:
- inadequate hygiene
- crowded households
- inadequate access to water
- inadequate access to and use of sanitation.
Distribution
Trachoma is hyperendemic in many of the poorest and most rural areas of Africa, Central and South America, Asia, Australia and the Middle East.
It is responsible for the blindness or visual impairment of about 1.9 million people. It causes about 1.4% of all blindness worldwide.
Overall, Africa remains the most affected continent and the one with the most intensive control efforts.
As of 5 October 2022, 15 countries – Cambodia, China, Gambia, Islamic Republic of Iran, Lao People’s Democratic Republic, Ghana, Malawi, Mexico, Morocco, Myanmar, Nepal, Oman, Saudi Arabia and Vanuatu – had been validated by WHO as having eliminated trachoma as a public health problem.
Economic impact
The burden of trachoma on affected individuals and communities is enormous. The economic cost in terms of lost productivity from blindness and visual impairment is estimated at US$ 2.9–5.3 billion annually, increasing to US$ 8 billion when trichiasis is included.
Prevention and control
Elimination programmes in endemic countries are being implemented using the WHO-recommended SAFE strategy. This consists of:
- Surgery to treat the blinding stage (trachomatous trichiasis);
- Antibiotics to clear infection, particularly mass drug administration of the antibiotic azithromycin, which is donated by the manufacturer to elimination programmes, through the International Trachoma Initiative;
- Facial cleanliness; and
- Environmental improvement, particularly improving access to water and sanitation.
Most endemic countries have agreed to accelerate the implementation of this strategy to achieve elimination targets.
Data reported to WHO by Member States for 2021 show that 69 266 people with trachomatous trichiasis were provided with corrective surgery in that year, and 64.6 million people in endemic communities were treated with antibiotics to eliminate trachoma. In 2019, when COVID-19 did not affect programmes’ ability to undertake community-based work, 92 622 people with trachomatous trichiasis were provided with corrective surgery, and 95.2 million people were treated with antibiotics.
Elimination efforts need to continue to ensure that we reach the target set by World Health Assembly resolution WHA 51.11, which is elimination of trachoma as a public health problem (1). Particularly important will be the full engagement of multiple actors involved in water, sanitation and socioeconomic development.
WHO response
WHO adopted the SAFE strategy in 1993. WHO’s mandate is to provide leadership and coordination to international efforts aiming to eliminate trachoma as a public health problem, and to report on progress towards that target.
In 1996, WHO launched the WHO Alliance for the Global Elimination of Trachoma by 2020. The Alliance is a partnership which supports implementation of the SAFE strategy by Member States, and the strengthening of national capacity through epidemiological surveys, monitoring, surveillance, project evaluation, and resource mobilization.
The World Health Assembly adopted resolution WHA51.11 in 1998, targeting the global elimination of trachoma as a public health problem with 2020 as the target date. The neglected tropical diseases road map 2021–2030, endorsed by the World Health Assembly in 2020 through its decision 73(33), sets 2030 as the new target date for global elimination.
(1) Elimination of trachoma as a public health problem is defined as: (i) a prevalence of trachomatous trichiasis “unknown to the health system” of <0.2% in adults aged ≥15 years (approximately 1 case per 1000 total population), and (ii) a prevalence of trachomatous inflammation – follicular in children aged 1–9 years of <5%, sustained for at least two years in the absence of ongoing antibiotic mass treatment, in each formerly endemic district; plus (iii) the existence of a system able to identify and manage incident trachomatous trichiasis cases, using defined strategies, with evidence of appropriate financial resources to implement those strategies.