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Table 4 Non-chemical triggers and COPD exacerbation (Weather, flu, and physical activity)

From: Low level air pollution and exacerbation of existing copd: a case crossover analysis

Variable type

Variable description

Odds ratio

95 % confidence interval

−2loglikelihood

Weather

Spent time in cold air/cold weather in past weeka

1.16

0.78

1.70

468

Spent time in hot air/hot weather in past weeka

0.50

0.34

0.75

457

Local Temperature (linear 7 day average)b

0.96

0.95

0.98

445

Local Temperature (categorical)c

 Cool/Cold

1.0

1.0

1.0

422

 Moderate

2.50

1.51

4.12

 Warm/Hot

0.55

0.36

0.84

Local Relative Humidity (linear 7 day average)b

0.98

0.96

1.01

471

Local Relative Humidity (categorical)c

 High

1.0

1.0

1.0

471

 Low

1.21

0.84

1.73

Season

Season, ref = summer

 Summer

1.0

1.0

1.0

417

 Spring

2.59

1.55

4.35

 

 Winter

2.38

1.37

4.11

 

 Fall

6.64

3.83

11.5

 

Acute Illness

Respiratory infection/cold in past weeka

8.14

4.67

14.2

396

Non-respiratory Illness in past weeka

1.65

0.67

4.05

422

Sinus infection in past weeka

2.55

1.20

5.44

461

Regional Flu Trends; New Englandd

3.78

1.54

9.28

463

Physical Activity

Total hours spent outside of the homea, e

0.99

0.99

1.00

469

Exercised in past weeka

0.60

0.39

0.93

462

  1. aBased on self-reports from exposure questionnaires
  2. bBased on 7-day averages using data from NOAA collected at Worcester Regional Airport
  3. cCategorical representation of variable based on cut-offs identified in restricted cubic splines
  4. dRegional proxy of flu from CDC data; represented by percent of weekly outpatient visits for influenza-like-illness in New England
  5. eEstimated as sum of “Hours Reported Outdoors”, “Hours Reported in a Vehicle”, and “Hours Reported Indoors but not at home”