Introduction
Methods
Description of the AusImmune Study
Study design considerations
-
Reducing the recruitment target to 150 participants: as a result, for a binary exposure of 30%, 40%, 50% prevalence, the minimum OR (for univariate associations between risk factors and the probability of developing PPMS) able to be detected with 80% power is 1.71, 1.68, 1.69 in the smaller sample of 150 cases and 558 controls than 1.50, 1.47, 1.47 in the original sample of 350 cases and 558 controls.
-
Expanding the age range to include people over the age of 60 years: we recruited additional participants who agreed to participate in the longitudinal study to also participate in the case–control study. We first invited those aged 60–62 years and gradually increased the cutoff from 60 to 62 to 65 years as required.
-
Due to logistical limitations and the high costs involved (using a commercial pathology service), biological sampling was discontinued and only samples from the first 48 participants were retained for future analysis.
-
With a dedicated longitudinal study becoming less feasible, it was decided to instead invite participants to become part of the Australian MS Longitudinal Study (AMSLS). The AMSLS is managed by author van der Mei. This study tracks patient-reported outcomes of Australian with MS over time and runs surveys on specific topics at annual or other intervals.
Case definition and confirmation of eligibility
Participant recruitment strategies
Participants recruited
PPMS POMS | PPMS and AusImmune POMS | MSBase All POMS | MSBase Australian POMS | AusImmune ROMS | Ausimmune Controls | |
---|---|---|---|---|---|---|
(n = 140) | (n = 155) | (n = 4094) | (n = 386) | (n = 204) | (n = 558) | |
Female, n (%) | 75 (53.6%) | 85 (54.8%) | 2146 (52.4%) | 222 (57.5%) | 166 (81.4%) | 436 (78.1%) |
Period of birth year, n (%) | ||||||
Before 1960 | 49 (35.0%) | 59 (38.1%) | 1565 (39.1%) | 153 (40.6%) | 44 (21.6%) | 169 (30.5%) |
1960–1969 | 72 (51.4%) | 74 (47.7%) | 1316 (32.9%) | 146 (38.7%) | 75 (36.8%) | 180 (32.4%) |
After 1970 | 19 (13.6%) | 22 (14.2%) | 1121 (28.0%) | 78 (20.7%) | 85 (41.7%) | 206 (37.1%) |
Year of birth, mean ± SD | 1962 ± 5.64 | 1962 ± 6.41 | 1964 ± 10.83 | 1962 ± 9.38 | 1967 ± 9.53 | 1965 ± 9.76 |
Age at first symptom (years), mean ± SD | 41.09 ± 8.11 | 41.44 ± 8.38 | 38.85 ± 10.11 | 40.47 ± 9.59 | 36.97 ± 9.52 | – |
Age at diagnosis (years), mean ± SD | 45.20 ± 7.96 | 45.15 ± 8.21 | 42.59 ± 10.25 | 43.71 ± 9.54 | 38.92 ± 9.64 | – |
Age at interview (years), mean ± SD | 55.29 ± 5.98 | 54.50 ± 6.97 | 49.85 ± 9.92 | 52.54 ± 8.68 | 37.73 ± 9.59 | 39.98 ± 9.75 |
Disease duration since first symptom (years), mean ± SD | 14.25 ± 7.76 | 13.08 ± 8.20 | 11.00 ± 7.90 | 12.08 ± 8.21 | 0.77 ± 1.03 | – |
Latitude banda | ||||||
≤ 28.9 °S | 20 (14.3%) | 27 (17.4%) | 212 (5.18%) | 43 (11.1%) | 69 (33.8%) | 183 (32.8%) |
28.9–34.6° S | 46 (32.9%) | 48 (31.0%) | 572 (13.97%) | 148 (38.3%) | 32 (15.7%) | 111 (19.9%) |
34.6–39.4° S | 51 (36.4%) | 56 (36.1%) | 948 (23.16%) | 172 (44.6%) | 49 (24.0%) | 148 (26.5%) |
> 39.4°S | 23 (16.4%) | 24 (15.5%) | 2364 (57.69%) | 23 (6.0%) | 54 (26.5%) | 116 (20.8%) |
Education levelb | ||||||
Primary school or less | 4 (2.9%) | 5 (3.3%) | 276(26.8%) | 0 | 3 (1.5%) | 16 (2.9%) |
Secondary/technical education | 91 (65.5%) | 101 (66.0%) | 296(28.7%) | 34 (45.9%) | 148 (73.3%) | 395 (71.3%) |
University | 42 (30.2%) | 45 (29.4%) | 459(44.52%) | 40 (54.1%) | 51 (25.3%) | 143 (25.8%) |
EDSS at interviewc, mean ± SD | 5.77 ± 1.67 | 5.63 ± 1.76 | 5.49 ± 1.83 | 5.72 ± 1.89 | 1.39 ± 1.24 | – |
Disability category at interview | ||||||
No disability (EDSS < 2) | 0 | 1 (0.7%) | 85 (2.5%) | 10 (3.6%) | 116 (59.8%) | – |
Mild disability (EDSS 2–3.5) | 22 (16.1%) | 29 (19.1%) | 554 (16.5%) | 38 (13.7%) | 70 (36.1%) | – |
Moderate disability (EDSS 4–6) | 35 (25.6%) | 39 (25.7%) | 1405 (41.7%) | 99 (35.7%) | 7 (3.6%) | – |
Severe disability (EDSS 6.5–9.5) | 80 (58.4%) | 83 (54.6%) | 1324 (39.3%) | 130 (46.9%) | 1 (0.5%) | – |