Table 2.
Estimates of the Point Prevalence and Severity of AA in the US
| AA Group | n | Prevalence Estimate | SALT Score |
|---|---|---|---|
| (95% CI) | Mean (SD) | ||
| Clinician-adjudicated (N=104)a | |||
| Point prevalence | |||
| AA overall | 19 | 0.21% (0.17, 0.25) | 44.4% (43.93) |
| “mild” AA | 11 | 0.12% (0.09, 0.15) | 8.8% (8.12) |
| “moderate to severe” AA | 8 | 0.09% (0.06, 0.11) | 93.4% (11.08) |
| AT/AUb | 4 | 0.04% (0.02, 0.06) | – |
| Sensitivity analysis of AA overall | |||
| Lower bound (indeterminate cases classified as non-AA) | 19 | 0.21% (0.17, 0.25) | – |
| Upper bound (indeterminate cases classified as AA) | 44 | 0.48% (0.42, 0.54) | – |
| Self-reported (N=45,016) | |||
| Point prevalence | |||
| AA overall | 511 | 1.14% (1.04, 1.24) | 25.4% (23.10) |
| “mild” AA | 463 | 1.03% (0.94, 1.12) | 19.3% (12.59) |
| “moderate to severe” AA | 48 | 0.11% (0.08, 0.14) | 84.7% (16.58) |
| AT/AU (SALT=100%)b | 18 | 0.04% (0.02, 0.06) | – |
| AT/AU (SALT≥90%)c | 23 | 0.05% (0.03, 0.07) | – |
| Lifetime prevalenced | |||
| AA overall | 1132 | 2.51% (2.37, 2.65) | – |
| AT/AU | 345 | 0.77% (0.69, 0.85) | – |
Notes: a104 participants uploaded photographs for clinician evaluation resulting in the following classifications by clinician majority: 19 AA cases, 60 non-AA cases, and 25 indeterminate cases (18 due to poor photo quality, 4 due to need for further testing, 3 due to poor photo quality or need for further testing). Using the clinician-adjudicated estimate for overall AA prevalence as an illustrative example, the proportion of clinician-adjudicated AA cases among those participants who uploaded photographs (19 out of 104) is multiplied by the estimated number of self-reported AA cases [(19 ÷ 104) × 511]. This calculation adjusts the numerator in the clinician-adjudicated prevalence estimate for those participants who did not upload photographs. To obtain the final overall estimate of 0.21%, the adjusted numerator is divided by an adjusted denominator which removes the 25 indeterminate cases {45,016 – [(25 ÷ 104) × 511]}. bAT/AU is a subset of moderate to severe AA and defined as self-reported SALT=100%. cAT/AU is a subset of moderate to severe AA and defined as self-reported SALT≥90%. dBased on ALTO alone and self-report of currently having AA or having AA in the past. AT/AU defined based on the ALTO; SALT was not used for the definition of AT/AU.
Abbreviations: AA, alopecia areata; ALTO, Alopecia Assessment Tool; AT, alopecia totalis; AU, alopecia universalis; AT/AU, AT and AU combined; CI, confidence interval; “mild” AA, self-reported SALT score ≤50% hair loss; “moderate to severe” AA, self-reported SALT score >50% hair loss; SALT, Severity of Alopecia Tool; US, United States.