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Occupational and Environmental Lung Disease |

Occupational Asthma*: A Longitudinal Study on the Clinical and Socioeconomic Outcome After Diagnosis FREE TO VIEW

Gianna Moscato, MD; Antonio Dellabianca, MD; Luca Perfetti, MD; Barbara Bramè, MD; Eugenia Galdi, MD; Rosanna Niniano, MD; Pierluigi Paggiaro, MD
Author and Funding Information

*From the Department of Allergy and Clinical Immunology (Drs. Moscato, Dellabianca, Perfetti, Brame, Galdi, and Niniano), Salvatore Maugeri Foundation, Occupational and Rehabilitation Clinic, IRCCS, Medical Center of Pavia, Specialization School of Allergology and Clinical Immunology, University of Pavia; and the Department of Cardiology, Angiology, and Pneumology (Dr. Paggiaro), University of Pisa, Italy.



Chest. 1999;115(1):249-256. doi:10.1378/chest.115.1.249
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Aim: To evaluate the clinical outcome and socioeconomic consequences of occupational asthma (OA).

Subjects and methods: Twenty-five patients with OA both to high- and low-molecular-weight agents (3 and 22, respectively) confirmed by specific inhalation challenge were followed up for 12 months after the diagnosis. Upon diagnosis, each patient received a diary on which to report peak expiratory flow rate (PEFR), symptoms, drug consumption, expenses directly or indirectly related to the disease, as well as information regarding personal socioeconomic status. At each follow-up visit (1, 3, 6, and 12 months), the patients underwent clinical examination, spirometry, methacholine (Mch) challenge, and assessment of diary-derived parameters and socioeconomic status. Asthma severity (AS) was classified into four levels, based on symptoms, drug consumption, and PEFR variability.

Results: At 12 months, 13 patients (group A) had ceased exposure; the remaining 12 patients (group B) continued to be exposed. At diagnosis, FEV1 percent and provocative dose causing a 20% fall in FEV1 (PD20) of Mch were lower in group A than in group B; patients of group A were also characterized by significantly higher basal AS levels. At 12 months, no significant variation in FEV1 percent or PD20 was found for either group, while AS levels improved in both groups, the change being more marked for group A than group B. Pharmaceutical expense at 12 months significantly (p < 0.05) decreased, as compared with the first month, in group A, whereas it tended to increase in group B. In group A, 9 of 13 subjects had reported a deterioration of their socioeconomic status as compared with 2 of 12 in group B (p < 0.01). A significant loss of income was registered in patients of group A (median 21.45, 25th to 75th percentiles 16.9 to 25.8 Italian liras × 106 on the year preceding diagnosis and 15.498, 10.65 to 21.087 Italian liras × 106 on the year after diagnosis; p < 0.01), whereas no significant change was seen for patients in group B.

Conclusions: In OA, cessation of exposure to the offending agent results in a decrease in asthma severity and in pharmaceutical expenses, but it is associated with a deterioration of the individual’s socioeconomic status (professional downgrading and loss of work-derived income). There appears to be a great need for legislation that facilitates the relocation of these patients.

Abbreviations: AS = asthma severity; HMW = high molecular weight; ITL = Italian liras; LMW = low molecular weight; Mch = methacholine; OA = occupational asthma; PD20 = provocative dose causing a 20% fall in FEV1; PEF, PEFR = peak expiratory flow (rate)

Figures in this Article

Occupational asthma (OA) is a respiratory disease characterized by variable bronchial obstruction and variable bronchial hyperreactivity caused by specific agents inhaled at work.1It is becoming increasingly recognized as a cause of work-induced respiratory disability, and there is evidence that it is becoming the most commonly compensated occupational lung disease.2 The social implications of this disease are thus becoming more and more important for the community.

Several studies have investigated the consequences of OA not only from a clinical but also from an economic point of view.3,,4,,5,,6,,7,,8 In most works, however, the data have been collected by recontacting the patients at a certain time after diagnosis.6,,8 In this study, we followed up prospectively at regular time intervals for 1 year a group of patients who were diagnosed in our center as suffering from OA due to various agents during 1992 to 1995. We report the individual and social disease-related costs along with the clinical and functional course of these patients.

Study Design

Subjects were examined at the time of diagnosis of OA and reevaluated at 1, 3, 6, and 12 months after diagnosis. Allergy skin tests were performed at time of diagnosis. For the duration of the study, all patients reported peak expiratory flow (PEF) values on a personal asthma diary together with symptoms, drug intake, medical events, and disease-related costs (see below). At time of diagnosis and at each following visit, clinical examination, spirometry, and bronchial challenge with methacholine (Mch) were performed and a questionnaire on symptoms, on working condition, as well as on the financial condition and disease-related costs was administered. The patients were told to abstain from the use of anticholinergic, adrenergic bronchodilator or sodium cromoglycate for at least 24 h and from slow-release theophylline or inhaled steroids for 48 h before these measurements and before Mch and specific challenges.

Subjects

All subjects receiving a diagnosis of OA in our center from 1992 to 1995 were invited to participate in this study. There were 32 subjects eligible: in all of them, diagnosis of OA was confirmed by means of specific inhalation challenge.9,,10,,11 All subjects underwent skin tests with a panel of 11 common allergen extracts11(Lofarma Allergeni; Milano, Italy): a subject was considered atopic if there was a personal history of eczema or allergic rhinitis, or there was a positive skin reaction (wheal diameter ≥ 3 mm) to one or more allergens.12

Questionnaire

At the time of diagnosis (baseline), patients underwent a careful interview. A detailed description of the current and previous work situation was obtained by the employees. The following were also recorded: duration of exposure, date of last exposure, time interval from first exposure to first symptoms, duration of symptoms from onset to first examination, and the date of the last symptoms.

Details on the current work situation of each patient were obtained from the employers, along with results of industrial hygiene surveys, when available, and with the safety data sheets of the products used by the patient at the workplace.

At the time of diagnosis, each patient was questioned about the total income of the year before diagnosis. At each follow-up visit, the income of the months preceding the visit was registered.

Asthma Severity

At each visit, on the basis of symptoms,β 2-agonist as occasion requires (prn) use, PEFR diurnal variability, recorded on the asthma diary during the previous month, and FEV1 percent of predicted, subjects were classified into four subgroups according to the National Institutes of Health classification of asthma severity:13 level 1 = mild intermittent; level 2 = mild persistent; level 3 = moderate persistent; and level 4 = severe persistent.

Spirometry

FEV1 and FVC were measured by a computerized water-sealed spirometer (BIOMEDIN; Padova, Italy). The predicted values were derived from Quanjer.14

Mch Inhalation Test

The details of the test have been reported previously.15 The patient is first administered five inhalations of phosphate-buffered saline solution. The latter are then followed by increasing, doubling doses of Mch, at 2-min intervals: dosage is increased from 30 to 3,200 μg as maximal cumulative dose or until a fall in FEV1 of 20% from the highest postsaline solution control level is observed. Two minutes after each series of inhalations, FEV1 was measured as described above. The Mch dose capable of causing a 20% fall in FEV1 (PD20) was calculated by interpolating on a semilogarithmic dose-response curve.

Socioeconomic Parameters

Direct and indirect disease-related costs and monthly work-derived income were analyzed. The following were considered as direct disease-related costs: medications (total cost of the drugs prescribed and taken by the patient for asthma maintenance), number of visits at physician’s office and number of medical house calls, number of visits at the emergency department, number of specialist consultations (excluding those scheduled at our center), number of days of hospitalization in the ICU, number of days spent in a pneumology department, number of day-hospital visits, number of days of nursing care, and patient transportation. As indirect costs, we considered the number of work days lost by the patients and their relatives.16,,17 At each visit, each patient was asked about his/her benefit claim (“have you been contacted by compensation board?”, ie, in Italy, the National Insurance Institute for Occupational Diseases, “have you been granted benefit?”).

Costs are expressed in Italian liras (ITL). Over the period of the study 1 US dollar approximately corresponded to 1,500 to 1,800 ITL.

Statistical Analysis

Data are presented as median, 25th and 75th percentiles in the following way (median, 25th percentile to 75th percentile). Statistical analysis was carried out by χ2 test, Wilcoxon matched-pairs signed-ranks test, and Mann-Whitney U test, where appropriate. Data derived from pulmonary function tests and Mch challenge tests at 12 months were compared with those obtained at diagnosis. The data derived from the patient diary (disease-related costs, drug intake) at 12 months were compared with the data obtained at the first follow-up visit (after 1 month). As concerns pharmaceutical expenses, these were calculated separately for the first month after diagnosis and for the last 6 months (monthly mean). The income of the month before diagnosis was compared with that reported for the 12th month after diagnosis. The income for the 12 months after the diagnosis (ie, the study period) was compared with that reported for the 12 months before the diagnosis.

A probability level < 5% was considered to be significant.

Three subjects refused to be enrolled in the study while four others did not come to control visits (two preferred to be followed up in another center, while two were no longer interested in participating in the study). The remaining 25 subjects completed the study. Among participants, OA was due to high-molecular-weight (HMW) agents in 3 subjects and to low-molecular-weight (LMW) agents in 22 (isocyanates in 9 of them) (Table 1). In the seven nonparticipants, the causal agents were LMW agents. Characteristics of participants at the time of diagnosis are reported in Table 2.

At the time of diagnosis, 23 the 25 subjects who participated in the study were currently exposed to the offending agent. Two subjects had been already moved to an area clear of exposure to the offending agent in the same plant 11 and 3 months before diagnosis, respectively. The number of nonexposed subjects changed from 15 at the first follow-up visit (1 month after diagnosis) to 11 at the 3-month visit, and 15 at the 6-month visit. At the 12-month follow-up visit, 13 patients (52%, group A) had definitively ceased exposure to the sensitizing agent. Of this group, six subjects (46%) had been relocated in another area within the plant, while the other seven had resigned and left the workplace. Of the latter, six (46%) had been subsequently reemployed but professionally downgraded; one (8%) remained unemployed.

At 12 months, 12 patients (48%, group B) continued to be exposed. Five of them (42%) had changed their task but still worked in the same area of the plant, reporting intermittent or lower exposure to the offending agent; the remaining 7 (58%) continued to perform the same task in the same work area, being exposed daily to the offending agent. Table 3 shows the clinical and functional parameters, in group A and B respectively, at diagnosis and after 12 months.

At the time of diagnosis, group A was characterized by a more severe disease in terms of asthma severity (AS) levels and by higher bronchial reactivity to Mch (Table 3). Baseline FEV1 was in the normal range in both groups but was significantly lower in group A. Group A and B were not significantly different as regards characteristics of patients and the other parameters of the disease.

A significant reduction (p < 0.001) in AS, as expressed by AS distribution, was seen in the whole group of subjects at the first month follow-up visit (Fig 1), independently from the continuing or removal from exposure. In the following months, no further significant variation in the overall AS distribution was found; nevertheless, the number of subjects who reported no symptoms progressively increased. All the latter belonged to the group of subjects who were removed from exposure. At 12 months, six subjects in group A had been asymptomatic for the last 6 months of the follow-up period, whereas seven patients still complained of asthma symptoms. Of the latter, four subjects showed no improvement in AS, as compared to the baseline, whereas in the remaining three, a lower level of AS was found. In group B, all 12 subjects were still symptomatic at 12 months; 7 patients had a lower level of AS as compared with baseline, whereas in 5 patients, AS level was unchanged. Due to these figures, the distribution of the level of AS was significantly different from baseline in both groups at 12 months (Table 3).

At 12 month follow-up visit, no significant change in FEV1 percent or PD20 from baseline was found for either group. Changes in PD20 from diagnosis to 12 months were not significantly different in group A vs group B, despite the apparently nonnegligible change of the median in group A (Table 3).

As concerns pharmacologic treatment, the proportion of subjects receiving inhaled steroids decreased from the time of diagnosis to 12 months in group A, while it slightly increased in group B, though neither change was statistically significant (Table 3).

With regard to the disease-related costs, only those of medications and lost work days were registered in a sufficient number of patients to allow statistical analysis. The other costs were from the follow-up program itself (scheduled visits). No cost due to unexpected events was registered in either group of patients. The pharmaceutical expenses, ie, the total cost of drugs taken by patients for asthma in ITL are reported in Table 3. In the first month after diagnosis, the pharmaceutical expense was significantly higher in group A than in group B. In the following months, a progressive decrease in group A and increase in group B, respectively, was observed. At 12-month follow-up visit, the amount of the expenses in group A was significantly lower than the baseline (first month follow-up visit) (−40.3%, p < 0.01), whereas no significant difference was found in group B.

The number of lost work days per month during the follow-up period decreased progressively: 2, 0 to 12.5 (mean, 7.5) days in the first month, 0, 0 to 2.75 (mean, 4.6) days during the second and the third month, 0, 0 to 0.9 (mean 3.8) days (p < 0.05 as compared with the first month) from the fourth to sixth month, and 0, 0 to 2.08 (mean, 2.9) days (p < 0.02 as compared with the first month) from the seventh to 12th month. In the last 6 months of follow-up, the total number of lost work days was higher in group A than in group B (0, 0 to 12, mean 28.8 vs 0.5, 0 to 13.75, mean 5.5, respectively). This difference, however, was not significant, because it was entirely due to long periods of unemployment of two subjects of group A.

At 12 months, 11 patients, 9 from group A and 2 from group B (p < 0.01), reported a deterioration of their economic condition. The remaining 14 patients reported no economic change.

Data on the annual income are reported in Table 3. At diagnosis, the annual income of the 12 months before diagnosis was similar in the two groups. At 12 months follow-up, the income of the 12 months after diagnosis of the patients in group A had significantly decreased as compared with the 12 months before diagnosis. No significant change was seen for patients in group B. The loss, as a percentage of annual income, was 26.6, 11.97 to 49.6 in group A and 0, 0.9 to 7.5 in group B (p < 0.01).

At the 12-month follow-up visit, seven patients (28%) were still awaiting to be contacted by the National Insurance Institute for Occupational Diseases. Eighteen patients (72%) had been contacted: 1 patient 1 month after diagnosis, 6 after 3 months, 11 after 6 months. Of the latter, seven patients (28%) had settled the claim for statutory compensation: four patients were awaiting compensation, three had already been granted disablement benefit. Five patients (20%) had had the claim rejected, six patients (24%) had claims that were outstanding. The amount of compensation awarded ranged from 67,000 to 522,000 ITL per month.

In this prospective study, we followed up a group of subjects with OA due to various agents at regular intervals of time for 1 year after the diagnosis, recording at each time point their clinical, functional, employment, and financial status.

Removal from exposure to the offending agent is recommended as the first-line measure for the management of OA.3,,4 Our data show that in Italy7 as in other countries5,,8 where this procedure is not mandatory, this occurs only in a limited proportion of subjects: at the 12-month follow-up, 52% of our subjects had ceased exposure to the offending agent, and 48% continued to be exposed. Moreover, in most cases, removal from exposure did not follow the diagnosis promptly, since 4 of 13 subjects continued to be exposed at reduced levels for up to 5 months.

In agreement with previous literature data,5,,6,,7 only about a quarter of our patients (6/25, 24%) could be relocated in the same factory without loss of employment. All these patients were employed in large corporations with an efficient medical service and the availability of areas completely clear of exposure to the causal agent. In our study, a consistent proportion of subjects who could not be relocated (28%) had to resign and look for another job, generally being professionally downgraded. One subject was unable to find another job and was still unemployed at the 12-month follow-up visit. The remaining subjects (12/25, 48%), worried by the difficulties in finding new employment, preferred not to leave their job, thus continuing to be exposed intermittently or daily. The proportion of subjects who remained exposed is higher than those reported by other authors:3,,5,,6,,8,,18 along with the different characteristics of studied populations, this finding could be accounted for by the current Italian socioeconomic condition that makes it difficult to find a new job.

Subjects who ceased exposure had more severe disease and lower PD20 of Mch at diagnosis than those who continued to be exposed. The age of the two groups was similar. These findings differ from those of previous studies3 in which the subjects who remained exposed were older and more seriously ill. Thus, in our data, the severity of disease at diagnosis seems an important determinant of the professional fate of the subjects. We suggest that in Italy, patients with OA cease exposure when are seriously ill, whereas, whenever possible, the subjects with milder asthma prefer to keep their original job, probably because of the economic difficulties related with a change of job. In addition, it is possible that the low intensity of the symptoms experienced by patients with mild OA, together with the symptomatic relief obtained by pharmacologic therapy, may lead these subjects to underestimate the consequences of continued exposure on their disease. Specific educational programs that increase the patient’s awareness regarding the health consequences of continued exposure, including cases of mild OA, would be useful.

An interesting finding of our study was that immediately after diagnosis, the degree of asthma severity ameliorated in the whole group of subjects, whether or not they were removed from exposure, probably as an effect of a better therapeutic regimen for these patients. This finding is in agreement with our recent findings that in Italy most subjects with OA are undertreated in the period before diagnosis.19However, in the follow-up period, our results confirm those of previous studies20,,21,,22,,23,,24 inasmuch that the cessation or continuation of exposure influenced the outcome of the disease. The outcome was generally good only in the group of patients who completely discontinued exposure (group A), even if, in agreement with several other reports,24,,25,,26,,27,,28 a complete recovery was observed only in a part of the patients in this group (46.2%). Although we did not find a statistically significant reduction in PD20, even in group A, one must consider that the statistical power of the study was low depending on the small number of subjects. Indeed, the loss at 12 months of the difference in PD20 between the two groups observed at diagnosis suggests a different trend in the evolution of the disease. Furthermore, the present study reports the results of a relatively short follow-up after the diagnosis (12 months) and we cannot exclude that the patients removed from exposure reporting only clinical improvement at 12 months show complete recovery after a prolonged follow-up.,29

In agreement with other recent studies,5,,6,,8 in our population, the short-term socioeconomic consequences of the diagnosis of OA were burdensome for the patients in group A, considering that job change resulted in professional downgrading or in periods of unemployment, and in significantly reduced income (income almost halved at 12 months). The loss of income in this group of patients who were no longer exposed was similar to that reported by Gannon et al5 in the United Kingdom and by Ameille et al8 in France. In contrast to our data, Gannon et al5 also reported a considerable loss of income for the patients who remained exposed, due to sickness, lack of promotion, or reduced opportunity for overtime. This fact did not occur in our subjects of group B, since they were able to maintain their job position, probably due to the lower degree of their asthma.

With regard to disease-related costs, only those costs concerning medications and loss of work days were registered in a sufficient number of patients to allow statistical analysis. No cost due to unexpected events (hospitalizations, visits at the emergency department, etc) was registered in either group of patients. In the first month after diagnosis, the pharmaceutical expense, as registered by the subjects in their diary cards, was significantly higher in group A, in agreement with the finding of a more severe disease at diagnosis in this group of subjects who needed more therapy. In the last 6 months of follow-up, the monthly pharmaceutical expenses of the two groups became similar due to a significant decrease in group A (−40.3% p < 0.01) and an increase in group B (+67.5%). These figures are mainly due to the fact that most patients from group A required bothβ 2-agonists and moderate-dose inhaled corticosteroids at diagnosis and, due to the clinical improvement, onlyβ 2-agonists as needed at 12 months, whereas in group B, a reduction of asthma severity was obtained by increasing the dosage of both types of drugs (β2-agonists and inhaled corticosteroids). Therefore our observation, if projected on a longer time interval, may indicate that cessation of exposure permits a substantial saving on pharmaceuticals. The loss of work days appeared higher in group A than in group B, though the difference was not statistically significant probably due to type II error. This finding can be accounted for by the fact that a number of patients in group A were unemployed for some time after having quit their job, and others had remained at home from their illness before definitive cessation of exposure. The temporary avoidance of exposure leads to high socioeconomic costs, eg, the economic compensation that is issued by the insurance companies for sick days.

The absence of other direct and indirect costs in our follow-up group suggests that a careful follow-up program can avoid the other costs that are generally related to severe disease, disease exacerbation, and uncontrolled asthma, like, for instance, hospital admissions.30

Lastly, our data also show the difficulties encountered by our patients in obtaining disablement benefit. The Italian system for compensation does not guarantee prompt and automatic compensation of subjects with OA. Because of the delay with compensation, along with the current Italian socioeconomic condition that makes it difficult to find a job, a number of our patients who resigned after the diagnosis of OA remained without any financial support for a long period of time, with serious socioeconomic consequences.

In conclusion, in this study, cessation of exposure after the diagnosis of OA occurred in the more seriously ill patients, probably because they could not continue their job. In all cases, the diagnosis was quickly followed by an improvement in AS, probably due to a better therapeutic regimen. But in a short follow-up period, only cessation of exposure allowed recovery or a persistent clinical improvement. Cessation of exposure was followed by a decrease in the pharmaceutical expense, but more importantly, it resulted in loss of income. The slow compensation procedures from the compensation board further aggravated the economic conditions of these subjects. Legislation is needed to make mandatory the relocation of patients with OA to safe areas in the workplace and without professional downgrading. Alternatively, when relocation is not possible and the worker cannot keep his or her job, legislation should be aimed at providing prompt income replacement indemnity and developing priority pathways for the reemployment of patients with OA.

Supported by grant ICS-57.3/RF92/719, from the Italian Ministry of Health.

Manuscript received November 26, 1997; revision accepted June 1, 1998.

Correspondence to: Gianna Moscato, MD, Salvatore Maugeri Foundation, Via Ferrata, 8 (loc. Cravino), 27100 Pavia, Italy; e-mail: allergo@fsm.it

Table Graphic Jump Location
Table 1. Etiologic Agents of Asthma in the 25 Subjects Participating in the Study
Table Graphic Jump Location
Table 2. Characteristics of Participants at Time of Diagnosis*
* 

Smoking habits: s = smokers, es = ex-smokers, ns = nonsmokers.

Asthma severity: 1 = mild intermittent; 2 = mild persistent; 3 =moderate persistent; 4 = severe persistent.

Type of response to SIC (specific inhalation challenge): i =immediate; d = dual; l = late.

Table Graphic Jump Location
Table 3. Comparison of Clinical, Functional, and Socioeconomic Data in Group A and Group B at Diagnosis and at 12 Months*
* 

Smoking habits: s = smokers, es = ex-smokers, ns = nonsmokers; M = male; F = female.

PEFR variability: 1: maximum amplitude < 20%; 2: 20% ≤ maximum amplitude ≤ 30%; 3: maximum amplitude > 30%.

Symptom severity: 1: symptoms up to once/week, nocturnal asthma up to 2 times/month; 2: symptoms up to once/day, nocturnal asthma > 2 times/month; 3: symptoms more than once/day, nocturnal asthma more than once/week; 4: continuous symptoms, frequent nocturnal asthma.

Asthma severity (referred to 1 month period) 1 = mild intermittent, 2 = mild persistent, 3 = moderate persistent, 4 = severe persistent.

Work-derived monthly income: income of the month before diagnosis and of the 12th month after diagnosis.

 

p < 0.05 χ2 test.

 

p < 0.05 Wilcoxon test.

§ 

p < 0.01 χ2 test.

 

p < 0.01 Wilcoxon test.

 

p < 0.05 Mann-Whitney U test.

# 

p < 0.01 Mann-Whitney U test.

Figure Jump LinkFigure 1.  Distribution of AS levels in the whole group at diagnosis, after 1 month (p < 0.001 vs diagnosis), after 6 months (p < 0.001 vs diagnosis), and after 12 months (p < 0.001 vs diagnosis).Grahic Jump Location
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Figures

Figure Jump LinkFigure 1.  Distribution of AS levels in the whole group at diagnosis, after 1 month (p < 0.001 vs diagnosis), after 6 months (p < 0.001 vs diagnosis), and after 12 months (p < 0.001 vs diagnosis).Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1. Etiologic Agents of Asthma in the 25 Subjects Participating in the Study
Table Graphic Jump Location
Table 2. Characteristics of Participants at Time of Diagnosis*
* 

Smoking habits: s = smokers, es = ex-smokers, ns = nonsmokers.

Asthma severity: 1 = mild intermittent; 2 = mild persistent; 3 =moderate persistent; 4 = severe persistent.

Type of response to SIC (specific inhalation challenge): i =immediate; d = dual; l = late.

Table Graphic Jump Location
Table 3. Comparison of Clinical, Functional, and Socioeconomic Data in Group A and Group B at Diagnosis and at 12 Months*
* 

Smoking habits: s = smokers, es = ex-smokers, ns = nonsmokers; M = male; F = female.

PEFR variability: 1: maximum amplitude < 20%; 2: 20% ≤ maximum amplitude ≤ 30%; 3: maximum amplitude > 30%.

Symptom severity: 1: symptoms up to once/week, nocturnal asthma up to 2 times/month; 2: symptoms up to once/day, nocturnal asthma > 2 times/month; 3: symptoms more than once/day, nocturnal asthma more than once/week; 4: continuous symptoms, frequent nocturnal asthma.

Asthma severity (referred to 1 month period) 1 = mild intermittent, 2 = mild persistent, 3 = moderate persistent, 4 = severe persistent.

Work-derived monthly income: income of the month before diagnosis and of the 12th month after diagnosis.

 

p < 0.05 χ2 test.

 

p < 0.05 Wilcoxon test.

§ 

p < 0.01 χ2 test.

 

p < 0.01 Wilcoxon test.

 

p < 0.05 Mann-Whitney U test.

# 

p < 0.01 Mann-Whitney U test.

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