Table 1. Potential risk factors for psittacosis among case-patients and controls in the Blue Mountains outbreak, Australia.
| Potential risk factor | Case-patients, N = 48 (%) | Controls, N = 310 (%) | Crude OR (95% CI)* | p value |
|---|---|---|---|---|
| Age group (y) | ||||
| 15–49 | 10 (21) | 155 (50) | Referent | |
| 50–64 | 27 (56) | 89 (29) | 4.7 (2.2–10.2) | 0.0007 |
| 65–75 | 11 (23) | 66 (21) | 2.6 (1.0–6.4) | 0.04 |
| Male sex | 30 (63) | 125 (40) | 2.5 (1.3–4.6) | 0.005 |
| Resident of the upper Blue Mountains | 42 (88) | 104 (34) | 13.9 (5.7–33.7) | <0.0001 |
| History of asthma | 1 (2) | 64 (21) | 0.08 (0.01–0.6) | 0.0009 |
| Employed | 28 (58) | 192 (62) | 0.9 (0.5–1.6) | 0.6 |
| Outdoor employment | 7 (15) | 39 (13) | 1.2 (0.5–2.8) | 0.64 |
| Bird contact | ||||
| Contact with caged or domestic birds | 3 (6) | 56 (18) | 0.3 (0.1–1.0) | 0.04 |
| Contact with poultry birds | 3 (6) | 28 (9) | 0.7 (0.2–2.3) | 0.80 |
| Visit to pet shop | 9 (20) | 39 (13) | 1.6 (0.7–3.6) | 0.25 |
| Visit to aviary | 0 (0) | 3 (1) | Incalculable | 1.0 |
| Visit to zoo | 0 (0) | 3 (1) | Incalculable | 1.0 |
| Visit to poultry farm | 0 (0) | 4 (1) | Incalculable | 1.0 |
| Level of contact with free-ranging (wild) birds† | ||||
| No contact | 9 (19) | 137 (44) | Referent | |
| Only indirect contact‡ | 15 (31) | 121 (39) | 1.9 (0.8–4.5) | 0.15 |
| Any direct contact§ | 24 (50) | 52 (17) | 7.0 (3.1–16.1) | <0.0001 |
| Yard exposures | ||||
| Lawn mowing | ||||
| Did not mow lawn | 21 (44) | 170 (55) | Referent | |
| Only mowed lawn with a grass catcher | 4 (8) | 75 (24) | 0.4 (0.1–1.3) | 0.14 |
| Mowed lawn without a grass catcher | 23 (48) | 65 (21) | 2.9 (1.5–5.5) | 0.0017 |
| Mowed lawn without a catcher for >1 hour | 15 (31) | 20 (6) | 6.6 (3.1–14.1) | <0.0001 |
| Pruning, cutting back branches | 21 (45) | 141 (47) | 1.0 (0.5–1.7) | 0.88 |
| Potting or weeding | 15 (31) | 155 (50) | 0.5 (0.2–0.9) | 0.02 |
| Watering yard | 24 (50) | 157 (52) | 0.9 (0.5–1.7) | 0.88 |
| Raking yard | 21 (45) | 106 (35) | 1.5 (0.8–2.8) | 0.25 |
| Soft landscaping | 12 (25) | 97 (31) | 0.7 (0.4–1.5) | 0.40 |
| Hard landscaping | 5 (10) | 17 (5) | 2.0 (0.7–5.7) | 0.19 |
| Mulching | 9 (20) | 56 (18) | 1.1 (0.5–2.4) | 0.84 |
| Using compost | 13 (27) | 49 (16) | 2.0 (1.0–4.0) | 0.07 |
| Using fertilizer | 9 (20) | 52 (17) | 1.2 (0.5–2.6) | 0.68 |
| Home renovations or demolition | 4 (9) | 29 (9) | 0.9 (0.3–2.7) | 1.00 |
| Bushwalking | 13 (28) | 91 (30) | 1.0 (0.5–1.9) | 1.00 |
| Current or ex-smoker | 23 (48) | 141 (45) | 1.1 (0.6–2.0) | 0.76 |
| General health self-rating | ||||
| Excellent to very good | 23 (48) | 182 (59) | Referent | |
| Good to fair | 18 (37) | 111 (36) | 1.3 (0.7–2.5) | 0.46 |
| Poor to very poor | 7 (15) | 17 (5) | 3.3 (1.2–8.7) | 0.02 |
| Yard attached to residence | 48 (100) | 302 (97) | Incalculable | 0.61 |
| Lived adjacent to bushland | 33 (68) | 184 (59) | 1.5 (0.8–2.9) | 0.27 |
| Lived in a house | 48 (100) | 305 (98) | Incalculable | 1.00 |
| Lived in the Blue Mountains <5 years | 11 (23) | 38 (12) | 2.1 (1.0–4.5) | 0.07 |
*OR, odds ratio; CI, confidence interval. †Chi-square test for linear trend = 24.5, p value < 0.001. ‡Indirect contact only with free-ranging (wild) birds: watching bird at bird feeder, watching birds in yard, seeing dead birds, watching birds in bird bath, bird flying in house. §Any direct contact with free-ranging (wild) birds: catching birds, clipping birds’ feathers, tending to sick birds, touching birds’ feathers, cleaning up or touching birds’ nest, cleaning up or touching bird droppings, handling dead birds.