Trachoma, caused by particular serovars of Chlamydia trachomatis, is the leading infectious cause of blindness. Infection is transmitted by ocular and nasal secretions that are passed from person to person on fingers, fomites (such as clothing) and eye-seeking flies (particularly Musca sorbens). (1,2,3) Ophthalmic infection is associated with an inflammatory conjunctivitis known as "active trachoma". Repeated episodes (4) of active trachoma can scar the eyelids. In some individuals, this leads to trachomatous trichiasis (TT), in which one or more eyelashes from the upper eyelid touch the eye. (5) TT is extremely painful. (6) It can be corrected surgically but, if left untreated, may lead to corneal opacification, vision impairment and blindness.
Trachoma can be eliminated as a public health problem with a package of interventions known as the "SAFE strategy", comprising surgery for TT, antibiotics to clear ocular C. trachomatis infection and facial cleanliness and environmental improvement (particularly improved access to water and sanitation) to reduce C. trachomatis transmission. Surgery should be offered to any individual with TT considered likely to benefit from an operation; the S component of the SAFE strategy is a public health intervention, including active case-finding if necessary, which is recommended when the prevalence of TT "unknown to the health system" (7) is [greater than or equal to] 0.2% among people aged [greater than or equal to] 15 years. The A, F and E components of SAFE are recommended for districts (usually with populations of 100 000-250 000) in which the prevalence of the active trachoma sign "trachomatous inflammation--follicular" (TF) (8) is [greater than or equal to] 5% in children aged 1-9 years. In those districts, all residents should usually be offered antibiotic treatment annually, the planned number of rounds depending on the most recent estimate of TF prevalence. (9) The criteria for elimination of trachoma as a public health problem are: (i) a prevalence of TT unknown to the health system of < 0.2% among people aged [greater than or equal to] 15 years and (ii) a prevalence of TF of < 5% among children aged 1-9 years in each formerly endemic district, plus (iii) evidence that the health system can continue to identify and manage incident cases of TT. (10)
Requirements for these interventions are determined by population-based prevalence surveys in districts suspected of being endemic at baseline, repeated at specified intervals after initiation of interventions. In particular, it is recommended that impact surveys be undertaken at least 6 months after the last planned annual round of antibiotic mass drug administration, in order to determine whether treatment should be continued or can safely be stopped. (11)
This report summarizes work conducted during 2021 to apply the SAFE strategy against trachoma. It includes estimates of the global population at risk of trachoma blindness based on district-by-district data submitted to WHO by national programmes. It is inherently complex to summarize the underlying epidemiological situation in this way, because for any district up to 3 estimates of prevalence may be valid at different times within a...