Demographic characteristics of the asthma cohort: 1997-2017.
A total of 158 records were collected for an asthma cohort which was analysed for a 20 years follow up period. Table 1 shows characteristics of the cohort focusing on smoking history, place of death and cause of death. The analysis included 153 asthma patients. The median age of cohort between sexes (male 18.5 [IQR 11-23]: female 19 [IQR13-25]; p=0.330). The total follow up period was 2208 person years (males [891 person years]: females [1317 person years]). Total mortality of 61.4% was reported among the participants in the cohort. There was no significant difference in the median age at death by sex 25.5[21-34], [p=0.340]. The median age at death by sex was 25 [19-32] for males and 26[21-37] for females. Participants in the cohort did not show any significant difference in their level of education by gender [p=0.474] and marital status [p=0.121].The study showed 46.2% of participants reported an income between US$201 and US$500, there was no significant difference in the level of income between males and females [p=0.232]. More males (53.2%) confirmed smoking history, there was a significant difference between males and females who never smoked [p=<0.001]. More (90.4%) asthma patients died at a health facility. There was no gender bias, males and females [p=0.677].
Causes of death among asthma patients
The main (46.8%) cause of death in the cohort of asthma patients was respiratory diseases followed by HIV, diabetes and kidney disease with (23.4%). Differences in the cause of death by gender were statistically significant in both respiratory and cardiovascular diseases (p=0.006), whilst mortality due to diseases of the Gastroesophageal reflux disease (GERD) and HIV, diabetes and kidney diseases were common in both sex (Table 1).
Table 1: Characteristics for the asthma patients cohort: 1997-2017
Category
|
Total
Sample (158)
|
Male (n=62)
39.3%
|
Female(n=96)
60.7%
|
p value
|
Age at enrolment median [IQR)
Total follow up period
Total Mortality n (%)
Mortality by Sex, n (%)
Male
Female
Age at death, median [IQR]
Level of Education n (%)
Never attended
Primary
Secondary
Tertiary
Marital Status
Divorced
Married
Single
Widowed
Income Level
<$100
$100-$200
$201-$500
>$500
Smoking history
Current/former
Never Smoked
Place of death
Home
Hospital/Clinic
Cause of death
Cardiovascular disease
Gastroesophageal Reflux disease
HIV, Diabetes, Kidney disease
Respiratory disease (Pneumonia, bronchitis,
|
19(13-25)
2208person years
94 (61.4)
37(61.7)
57(61.3)
25.5[21-34]
6(3.8)
12(7.6)
124(78.5)
16(10.1)
20(12.7)
69(43.7)
42(26.6)
27(17.1)
37(23.4)
30(19.0)
73(46.2)
18(11.4)
56(35.4)
102(64.6)
9(9.6)
85(90.4)
9(9.6)
19(20.2)
22(23.4)
44(46.8)
|
18.5(11-23)
891person years
-
25[19-32]
2(3.2)
7(11.3)
46(74.2)
7(11.3)
7(11.3)
27(43.6)
21(33.9)
7(11.3)
14(22.6)
13(21.0)
25(40.3)
10(16.1)
33(53.2)
29(46.8)
4(10.8)
33(89.2)
0
6(16.2)
8(21.6)
23(62.2)
|
19(13-25)
317person years
-
26[21-37]
4(4.2)
5(5.2)
78(81.3)
9(9.4)
13(13.5)
42(43.8)
21(21.9)
20(20.8)
23(24.0)
17(17.7)
48(50.0)
8(8.3)
23(24.0)
73(76.0)
5(8.8)
52(91.2)
9(15.8)
13(22.8)
14(24.6)
21(36.8)
|
0.330
-
0.960
0.340
0.748
0.158
0.289
0.699
0.685
0.980
0.096
0.121
0.839
0.606
0.232
0.131
<0.001
<0.001
0.677
0.001
0.314
0.670
0.002
|
Clinical characteristics of the asthma patients
Table 2 shows the clinical characteristics of the asthma patients. Controlled asthma was defined as the extent to which the various manifestations of asthma are reduced or removed by asthma treatment. The proportion of patients who died with asthma during the period of interest was significantly higher in those with uncontrolled asthma [p=0.040]. Participants in the cohort did not show any significant difference in the regularity of their use of maintenance medications [p=0.421] and adherence to asthma medications [p=0.476].A history of asthma exacerbation significantly correlated with mortality [p=<0.001]. When compared to use of beclomethasone inhaler, participants who had used the Seretide accuhaler were significantly less likely to have died during the follow up period [p=0.026]. Majority (57.5%) of those who died with asthma had a history of atopy (eczema/hay fever). There was no significant differences in the proportion of those asthma patients who died whilst on asthma medications. Majority (63.9%) reported not having a history of emphysema/chronic bronchitis.
Table 2: Clinical characteristics of the asthma patients (cohort) n=153
Category
|
Dead
n=94
|
Alive
n=59
|
P value
|
Asthma controlled
Yes
No
Regular use of maintenance medications
Yes
No
Adherence to asthma medications
Yes
No
History of Exacerbation
Yes
No
Use of corticosteroid inhaler
Yes
No
Type of corticosteroid inhaler used
Beclamethasone
Seretide accuhaler
History of emphysema/chronic bronchitis
Yes
No
History of Atopy
Eczema/ Hay fever
No
Medications
Ever taken Beclamethasone
Ever taken Ipratropium
Ever taken Prednisolone
Ever taken theophylline
Ever taken 3 or more medications
|
41(43.6)
53(56.4)
59(62.8)
35(37.2)
53(56.4)
41(43.6)
78(83.0)
16(17.0)
53(56.4)
41(43.6)
31(58.5)
22 (41.5)
29(30.9)
65(69.1)
54(57.5)
40(42.6)
9(9.6)
14(14.9)
40(42.6)
17(18.1)
14(14.9)
|
36(61.0)
23(39.0)
38(64.4)
21(35.6)
33(55.9)
26(44.1)
43(72.9)
16(27.1)
33(55.9)
26(44.1)
14(42.4)
19 (57.6)
28(47.5)
31(52.5)
26(44.1)
33(55.9)
4(6.8)
5(8.5)
27(45.8)
11(18.6)
12(20.3)
|
0.018
0.421
0.476
0.067
0.476
0.026
0.294
0.05
0.546
0.243
0.697
0.978
0.387
|
Health services utilisation by asthma patients
The significant factors associated with mortality were not seeing the same doctor or specialist doctor and a history of having visited a doctor for their asthma in the past 2 years [p=<0.001]. Those who visited emergency department for severe asthma attack and also those who got admitted to hospital because of asthma attack had a significantly high mortality rate [<0.001].
Table 3 Health Service Utilisation by asthma patients
Category
|
Dead
n=94
|
Alive
n=59
|
p value
|
See same doctor for asthma
Yes
No
See specialist doctor for asthma
Yes
No
Visited a doctor for asthma in the past 2 years
Yes
No
Visited emergency department for asthma in the past two years
Yes
No
Admitted to hospital for asthma treatment in the past 2 years
Yes
No
|
6(6.4)
88(93.6)
23(24.5)
71(75.5)
88(93.6)
6(6.4)
80(85.1)
14(14.9)
86(91.5)
8(8.5)
|
1(1.7)
58(98.3)
13(22.0)
46(78.0)
55(93.2)
4(6.8)
52(88.1)
7(11.9)
50(84.8)
9(15.2)
|
0.088
<0.001
<0.001
<0.001
<0.001
|
The Kaplan Meier survival curves (Fig 1) showed significant differences of smokers and non smokers in the first 10 years follow up period (p=0.004). However, there was no significant difference for the last 10 years follow up period. Smokers had a median survival of 15 person years while the non smokers had a median survival time of 16 person years
Kaplan Meier survival curves for clinical characteristics of asthma patients.
The Kaplan Meier survival curves (Fig 2) below showed significant differences (p=0.009) in survival during a follow up period of 20 years. Patients who had controlled asthma had a median survival time of 19 person years compared to those uncontrolled who had a median survival time of 13 person years. The mortality rate amongst those controlled was 4/100 whereas for those uncontrolled had a mortality rate was 6/100 over the 20 year follow up period.
The log-rank test for equality of survival times between patients with asthma who used Beclomethasone inhaler and Seretide Accuhaler showed that Seretide Accuhaler users had significantly higher survival (p=0.04). The use of Seretide Accuhaler resulted in significantly lower mortality rate (4/100) compared to Beclamethasone inhaler whose mortality rate was 6/100 over the 20 year follow up period (p=0.04). (Fig 3). Review of records on the use of Seretide Accuhaler and Beclamethasone inhaler showed that patients who were using Seretide Accuhaler had it prescribed in the private setting.
There were significant differences between asthma patients who indicated history of eczema, hay fever and lack thereof (p=0.03) (Fig 4). However, the incidence rates of those with a history of eczema or those without was the same (4/100). Patients who had a history of hay fever had the least median survival time (12 person years) for the follow up period of 20 years while those with with history of eczema had a median survival time of 16 person years.
The participants’ survival time also differed by diagnosed conditions. Those diagnosed with respiratory conditions (Pneumonia and Bronchitis) had the highest incidence death rate of 6/100 patients over the 20-year follow-up period. Gastroesophageal reflux diseases had an incidence death rate of 5/100 patients, whilst the lowest was in cardiovascular diseases (3/100 patients). HIV, diabetes and kidney diseases contributed to combined incidence death rate of 4/100 patients of the follow-up period.
Survival times for asthma patients according to health services utilization
Regardless of the log-rank test showing lack of significance between survival times of participants who see the same doctor or different doctors over the 20 year follow-up period, seeing the same doctor had a mortality rate of 5/100 compared to those participants who sought help from different doctors whose mortality rate was 8/100 persons over a 20 year follow-up period. Seeing a specialist doctor in the first 10 years had a better survival compared to seeing the specialist doctor during the last 10 years. Those who did not see a specialist doctor had a median survival time of 17 person years. However, there were no significant differences (p=0.647).
The log-rank test for identifying differences in Kaplan Meier Curves on asthma patients according to doctor visited in the past 2 years did not show significant differences. However, the follow-up period of 5 and 15 years depicted some significant difference between those who visited a doctor in the past two years and those who did not visit a doctor in the past two years.
Investigation on the clinical characteristics on the survival of asthma patients showed that uncontrolled asthma was significantly contributing to death, with the hazard ratio of 1.68(p=0.01). Thus, a patient with uncontrolled asthma was 68% more likely to die compared to those who had it under control. Significant hazard ratios also included the use of Beclamethasone inhaler as compared to Seretide accuhaler. Patients who used Beclamethasone inhaler were 1.75 times more likely to die at any given time over the follow-up period as compared to those using seretide accuhaler. Also, patients with a history of atopy (Hay fever) were 1.93 times more likely to die compared with to those without a history of atopic conditions. Furthermore, the use of Ipratropium was a borderline significant hazard ratio with an estimate of 1.98(p=0.07).
In bivariate analysis, seeing the same primary care doctor and a specialist doctor were a risk factor. Those patients seeing different doctors were 48% less likely to die compared to those who were being seen by the same doctor and referred to a specialist doctor. (Table 5).
Table 5: Bivariate cox regression models for demographic characteristics, clinical characteristics, health service utilisation and asthma self-management
Variable
|
Hazard Ratio (95% CI)
|
P-value
|
Demographic Characteristics
|
Gender
Female
Male
Employment Status
Unemployed
Employed
Income Status
$100-$200
$201-$500
<$100
>$500
Smoking History
Non-Smoker
Smoker
|
Reference
0.96(0.63-1.45)
Reference
0.66(0.45-1.01)
Reference
1.37(0.73-2.61)
3.08(1.57-6.04)
1.89(0.83-4.30)
Reference
1.16(0.76-1.78)
|
0.83
0.05*
0.33
0.001*
0.14
0.49
|
Clinical Characteristics
|
Asthma Control
Yes
No
Regular use of maintenance medications
Yes
No
Adherence to asthma medications
Yes
No
Use of corticosteroids inhalers
Seretide Accuhaler
Beclamethasone inhaler
History of atopy
No
Eczema
Hay fever
Asthma medications used
Ever taken >3
Prednisolone
Theophylline
Beclomethasone
Ipratropium
|
Reference
1.68(1.11-2.52)
Reference
1.09(0.72-1.66)
Reference
0.99(0.66-1.49)
Reference
1.75(1.01-3.04)
Reference
1.16(0.72-1.88)
1.93(1.17-3.18)
Reference
1.24(0.67-2.28)
1.31(0.64-2.65)
1.45(0.63-3.35)
1.98(0.94-4.16)
|
0.01*
0.68
0.98
0.045*
0.54
0.01*
0.49
0.46
0.39
0.07
|
Health service utilization
|
See same doctor for asthma
Yes
No
See specialist for severe asthma
Yes
No
Admitted to hospital in the past 2 years
No
Yes
Visited a doctor in the past 2 years
Yes
No
|
Reference
0.52(0.23-1.19)
Reference
1.11(0.69-1.77)
Reference
1.39(0.68-2.88)
Reference
1.11(0.48-2.54)
|
0.12
0.68
0.37
0.81
|
Asthma Self-Management
|
Know which medications to take in severe asthma
Yes
No
Have written down instructions about when to call for help in severe asthma attack
Yes
No
Know when to call for help in a severe asthma attack
Yes
No
|
Reference
1.06(0.66-1.70)
Reference
0.87(0.55-1.40)
Reference
0.91(0.61-1.37)
|
0.80
0.58
0.65
|
Multivariate cox proportional hazards analysis
A multivariate cox proportional hazard analysis showed that after controlling for smoking, history of atopy, the above factors were significant to explain the survival of asthma patients. The model showed that the most significant risk factor for mortality was seeing different doctors (p=0.005). However, those who were admitted in the past 2 years were 3.6 times more likely to die due to uncontrolled asthma after adjusting for other factors (smoking, history of atopy