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Review
. 2004 Oct;17(4):982-1011, table of contents.
doi: 10.1128/CMR.17.4.982-1011.2004.

Diagnosis and assessment of trachoma

Anthony W Solomon  1 , Rosanna W Peeling, Allen Foster, David C W Mabey
Affiliations
Review

Diagnosis and assessment of trachoma

Anthony W Solomon et al. Clin Microbiol Rev. 2004 Oct.

Abstract

Trachoma is caused by Chlamydia trachomatis. Clinical grading with the WHO simplified system can be highly repeatable provided graders are adequately trained and standardized. At the community level, rapid assessments are useful for confirming the absence of trachoma but do not determine the magnitude of the problem in communities where trachoma is present. New rapid assessment protocols incorporating techniques for obtaining representative population samples (without census preparation) may give better estimates of the prevalence of clinical trachoma. Clinical findings do not necessarily indicate the presence or absence of C. trachomatis infection, particularly as disease prevalence falls. The prevalence of ocular C. trachomatis infection (at the community level) is important because it is infection that is targeted when antibiotics are distributed in trachoma control campaigns. Methods to estimate infection prevalence are required. While culture is a sensitive test for the presence of viable organisms and nucleic acid amplification tests are sensitive and specific tools for the presence of chlamydial nucleic acids, the commercial assays presently available are all too expensive, too complex, or too unreliable for use in national programs. There is an urgent need for a rapid, reliable test for C. trachomatis to assist in measuring progress towards the elimination of trachoma.

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Figures

FIG. 1.
FIG. 1.
Model of the elementary body cell wall, after Everett and Hatch (67). LPS, lipopolysaccharide.
FIG. 2.
FIG. 2.
Upper tarsal conjunctival zones used for scoring F in the FPC system. “Zones are defined by two imaginary lines which, as viewed on the everted tarsal surface, are approximately parallel with the upper tarsal border and curve upward towards their lateral extremities… Zone 1 includes the entire upper tarsal border and adjacent lateral tarsal surface; zone 2 occupies the area between zones 1 and 3 and extends to the lateral quarters of the lid margin; zone 3 includes the tarsal conjunctiva adjacent to the central half of the lid margin and, at its center, covers just less than half the vertical extent of the tarsal surface” (reference , p. 14). Modified by Matthew Burton and reproduced with the permission of M. Burton and the World Health Organization.
FIG. 3.
FIG. 3.
WHO simplified system. (a) Normal conjunctiva, showing area to be examined. (b) Follicular trachomatous inflammation (TF). (c) Intense trachomatous inflammation (TI) (and follicular trachomatous inflammation). (d) Conjunctival scarring (TS). (e) Trichiasis (TT). (f) Corneal opacity (CO). Reproduced with the permission of the World Health Organization.
FIG. 4.
FIG. 4.
PCR profile. The signal (shown on the vertical axis) is related to the amount of amplified product and has been acquired once per cycle. 1, background phase; 2, exponential phase; 3, plateau phase.
FIG. 5.
FIG. 5.
Hypothesized models for the relationship between infection, disease, and test positivity following introduction of C. trachomatis into the conjunctival sac (↓ = C. trachomatis inoculum). (a) Two inocula fail to establish productive conjunctival infection. (b) Inoculum establishes productive infection, which results in the appearance of clinical signs of active trachoma. (c) Repeated reinfection causing sustained active disease, but resulting in shortened duration of infection and nucleic acid amplification test positivity through development of protective immunity. (d) Persistent infection (marked *). (e) Cryptic infection (marked **). NAAT, nucleic acid amplification test.
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References

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