Abstract
We investigated the prevalence of chronic cough and its association with work ability and sick leave in the general population.
Data were analysed from the Respiratory Health In Northern Europe (RHINE) III cohort (n=13 500), of which 11 252 participants had also participated in RHINE II 10 years earlier, a multicentre study in Northern Europe. Participants answered a questionnaire on chronic cough, employment factors, smoking and respiratory comorbidities.
Nonproductive chronic cough was found in 7% and productive chronic cough in 9% of the participants. Participants with nonproductive cough were more often female and participants with productive cough were more often smokers and had a higher body mass index (BMI) than those without cough. Participants with chronic cough more often reported >7 days of sick leave in the preceding year than those without cough (“nonproductive cough” 21% and “productive cough” 24%; p<0.001 for comparisons with “no cough” 13%). This pattern was consistent after adjusting for age, sex, BMI, education level, smoking status and comorbidities. Participants with chronic cough at baseline reported lower work ability and more often had >7 days of sick leave at follow-up than those without cough. These associations remained significant after adjusting for cough at follow-up and other confounding factors.
Chronic cough was found in around one in six participants and was associated with more sick leave. Chronic cough 10 years earlier was associated with lower work ability and sick leave at follow-up. These associations were not explained by studied comorbidities. This indication of negative effects on employment from chronic cough needs to be recognised.
Abstract
In an adult general population, one in six reports chronic cough. Chronic cough, current and a decade earlier, is associated with increased sick leave days and decreased work ability in middle-aged adults from the general Northern European population. https://bit.ly/35Iz694
Introduction
Chronic cough in adults can be productive or nonproductive. Both types can be associated with a number of respiratory diseases or be idiopathic. Common causes of chronic nonproductive cough are gastro-oesophageal reflux, asthma and chronic rhinosinusitis [1]. Chronic productive cough, regularly leading to the expectoration of sputum, is associated with smoking and lung conditions such as chronic obstructive pulmonary disease (COPD), chronic bronchitis and bronchiectasis [2–4].
Although the definition of chronic cough in epidemiological studies varies, an average global prevalence of ∼10% has been reported, with a significant variation between countries [1, 5]. Many of these studies do not differentiate clearly between productive and nonproductive cough, but one Nordic study found the ratio between the two to be 1:1 in young adults [6]. Few studies have addressed the long-term prognosis of this condition. In a small study on patients with well-characterised idiopathic chronic cough, a majority reported persisting symptoms at 7-year follow-up [7]. Similar results have been reported in a small study by Koskela et al. [8], where almost half of the participants with chronic cough still suffered from the condition at 5-year follow-up. The development of chronic cough over time in the general population has not been investigated.
Chronic cough has been reported to be associated with impaired health-related quality of life, including both physical and psychological components [1, 9]. However, even though the condition is relatively common in people of working age, studies on employment and work-related factors of chronic cough are scarce [10]. In a Finnish study of public service employees, around half of participants with chronic cough reported at least 1 week of sick leave during the preceding 12 months compared with around one-third of participants without chronic cough [11]. Poor work ability is predictive of early retirement and negative health outcomes, and therefore needs to be addressed in a timely manner [12–14].
Our primary aim was to investigate the prevalence progression of chronic cough in a general adult Northern European population, and its association with work ability and days of sick leave, both cross-sectional and over a 10-year period. Our secondary aim was to investigate the progression of chronic cough over a 10-year period.
Methods
This study was both a cross-sectional and a prospective general population questionnaire study. We used data from the Respiratory Health In Northern Europe (RHINE) III study, a multicentre questionnaire study from 2010 to 2012, and the RHINE II study, performed in 1999–2000, aiming to study various aspects of respiratory health (www.rhine.nu) [15]. The study protocol has been described in detail previously [15, 16]. The participants, then aged 20–44 years, were originally recruited randomly from the general population to the European Community Respiratory Health Survey (ECRHS) I in 1990 (www.ecrhs.org) [16]. ECRHS I participants from the study centres in Sweden, Norway, Denmark, Iceland and Estonia were identified as the RHINE cohort [17]. The participants answered the questionnaires for RHINE II and RHINE III via postal mail. All participants from the RHINE centres in 1990 (n=21 802) were eligible for RHINE III.
In total, 13 500 participants answered the questions in RHINE III on cough and were therefore eligible for the cross-sectional part of this study (62% participation rate). Of these, 11 252 participants had also participated in RHINE II and were thus eligible for the longitudinal part of the study (figure 1). The differences between responders and nonresponders in the follow-up study have been studied specifically, and interestingly the baseline prevalence of respiratory symptoms among long-term participants was somewhat lower than in the whole baseline population. Otherwise, differences were minimal [15].
Data available for the current study. RHINE: Respiratory Health In Northern Europe. Data on employment were only available in RHINE III (follow-up), therefore cross-sectional analysis was performed on RHINE III (n=13 500), and longitudinal analysis on RHINE II and III (n=11 252).
The RHINE II and RHINE III questionnaires included identical questions on cough, age, sex, weight, height, smoking habits and comorbidities, including airway diseases. Questions on education level, work ability and sick leave were included only in RHINE III.
Each participant gave informed consent. Local ethics committees approved the study for each centre.
Chronic cough
Chronic cough was defined as an affirmative answer to the question “Have you in recent years been troubled by a protracted cough?”. Participants reporting chronic cough were identified as having productive cough if they answered yes to the question “Do you usually cough up phlegm or do you have phlegm in your chest that is difficult to cough up?”; otherwise, they were considered to have nonproductive cough.
Definitions of comorbidities
Current asthma was defined in the same manner as previously reported, by a positive response to the question “Have you had an attack of asthma in the last 12 months?” and/or a positive response to the question “Are you currently taking any medicine (including inhalers, aerosols or tablets) for asthma?” [18]. COPD was defined as an affirmative response to the question “Has a doctor ever told you that you have COPD?”. Chronic rhinosinusitis was defined as reporting two or more of the following four symptoms for ≥12 weeks in the preceding 12 months: nasal congestion, facial pain/pressure, nasal discharge or reduction/loss of smell [19]. Gastro-oesophageal reflux was defined as reporting recumbent chest burn or regurgitation once a week or more [20].
Sick leave and work ability
The questions on sick leave and work ability were included only in RHINE III. Current work status was reported by answering yes or no to the question “Are you currently working?”. In total, 110 participants did not answer and 1884 reported not currently working (for distribution between cough groups, see table 1). The remaining 11 506 currently working participants were included in the analyses on sick leave and work ability. Of them, 9671 had also participated in RHINE II.
Population characteristics
The questions on work ability and sick leave were taken from the validated Work Ability Index (WAI) [21, 22]. The WAI includes a question on “current work ability compared with the life-time best”, which yields a value from 0 to 10 (“unable to work” to “work ability at its best”), defined as the work ability score. The score was classified into four groups as described in the original publication (poor=0–5, moderate=6–7, good=8–9 and excellent=10) [23]. This single question is reported to reflect the total WAI score reasonably well [21].
The questions on sick leave days during the preceding 12 months had five response options, with intervals as: 0, 1–7, 8–30, 31–90 and 91–365 days.
Participants also reported if they had ever changed job because of breathing problems by answering yes or no to the question “Have you ever changed job because the job affected your breathing?”.
Statistical analysis
The data were analysed using Stata version 16 (StataCorp, College Station, TX, USA). First, descriptive statistics were calculated for the whole cohort and the cough subgroups. Thereafter, a two-sided Chi-squared test was used to compare differences in prevalence between groups. For adjusted and stratified analyses, we used a logistic regression to adjust for possible confounding factors, defined a priori. Confounding factors were determined to be study centre, age, sex, body mass index (BMI), education level, smoking status, and the comorbidities current asthma, COPD, chronic rhinosinusitis and gastro-oesophageal reflux. Analyses on sick leave days and work ability were performed on participants currently working.
For analysis of longitudinal data, multivariate logistic regression was used to analyse associations between cough at baseline and follow-up and employment outcomes at follow-up (sick leave and work ability). A binomial log-linked generalised estimating equation was used only to analyse change in cough prevalence. Statistical significance was defined as an α-level of 0.05.
Results
Cross-sectional analysis
Prevalence of chronic cough
In total, 7% of the participants reported a chronic nonproductive cough and 9% reported a chronic productive cough, yielding 16% reporting chronic cough. Participants with a chronic nonproductive cough were more often female and more often reported hypertension, but other characteristics were similar compared with those without cough (table 1). Participants with a chronic productive cough were more often smokers, had a higher BMI, and more often had cardiovascular comorbidities and diabetes than those without cough. They also had a lower level of formal education compared with those without cough (table 1).
Individuals with a chronic nonproductive cough were less likely to have an identifiable potential cause of their cough than those with a chronic productive cough. Among those with a chronic nonproductive cough, less than one out of three had asthma, COPD, chronic rhinosinusitis or gastro-oesophageal reflux. Among those with a chronic productive cough, roughly one in two had an identifiable potential cause for cough (table 1).
Employment
The self-assessed work ability score among participants currently working was somewhat decreased among participants with chronic cough, especially among those with productive cough (figure 2a). Significantly fewer participants with chronic cough reported excellent work ability compared with those without cough (“no cough” 60%, “nonproductive cough” 49% and “productive cough” 41%; p<0.005 for all comparisons). This was consistent after adjusting for confounding factors.
Self-reported a) current work ability score and b) sick leave from work in the preceding 12 months among participants without cough, with chronic nonproductive cough or with chronic productive cough. Work ability is graded on a scale from 0 to 10, with 10 being self-assessed best work ability in the participant's own work life (poor=0–5, moderate=6–7, good=8–9 and excellent=10). Only participants currently working were analysed (n=11 250).
Among participants currently working, 21% of those with chronic nonproductive cough had been on sick leave for >7 days in the preceding year compared with 13% among those without cough (p<0.001). The corresponding figure for those with chronic productive cough was 24% (p<0.001 compared with those without cough) (figure 2b). This pattern was consistent after adjusting for confounding factors (adjusted OR compared with those without cough: “nonproductive cough” 1.48 (95% CI 1.19–1.83) and “productive cough” 1.60 (95% CI 1.31–1.95)). The association between chronic cough and sick leave did not differ significantly between those with or without an identifiable cause of their cough (data not shown). The pattern was also consistent when stratified by current asthma. However, when stratified by sex, nonproductive cough was no longer significantly associated with increased sick leave among males (figure 3).
Odds ratios for reporting a) >7 days of sick leave and b) excellent work ability among currently working (n=11 250) participants with chronic nonproductive or productive cough compared with participants without cough, analysed specifically for each sex, and adjusted for study centre, age, body mass index, education level, smoking status, and the comorbidities current asthma, chronic obstructive pulmonary disease, chronic rhinosinusitis and gastro-oesophageal reflux.
Participants with chronic nonproductive and productive cough had more often changed job because of breathing problems (table 1). This pattern was consistent after adjusting for confounding factors (adjusted OR compared with those without cough: “nonproductive cough” 1.86 (95% CI 1.13–3.06) and “productive cough” 2.07 (95% CI 1.38–3.09)).
Longitudinal analysis
Prevalence of chronic cough
A small, nonsignificant increase in the prevalence of chronic cough was found among participants with both baseline and follow-up data (nonproductive cough from 6.3% to 6.8% (p=0.11) and productive cough from 8.5% to 9.1% (p=0.095)). Among participants with nonproductive cough at baseline, two-thirds did not report any cough at follow-up, and in those with persistent cough, one out of two had developed productive cough (table 2). Among participants with a chronic productive cough at baseline, one in two did not report cough at follow-up and only one in four of those who still had cough had developed nonproductive cough (table 2).
Change in self-reported cough between baseline and follow-up
Employment
Chronic cough at baseline was associated with decreased work ability and increased sick leave from work at follow-up. After adjusting for confounding factors, both productive and nonproductive cough, at both baseline and follow-up, were found to associate with decreased work ability and increased sick leave from work at follow-up compared with those without cough (figure 4). However, the association between productive cough at baseline and increased sick leave from work at follow-up was not significant.
Odds ratios for reporting a) >7 days of sick leave and b) excellent work ability at follow-up, by self-reported cough at baseline and follow-up (n=9464). Adjusted for current asthma, baseline and change in body mass index, chronic obstructive pulmonary disease at follow-up, chronic rhinosinusitis at follow-up, gastro-oesophageal reflux at follow-up, age, sex, and centre. Only participants currently working were analysed.
Discussion
In this multicentre population-based study, the prevalence of self-reported, troublesome chronic cough was 16%, which despite the ageing of the study population did not increase significantly over a 10-year period. To the best of our knowledge, this is the first study to report on work ability and sick leave among individuals with chronic cough in the general population. Among participants currently working, those with chronic cough had lower work ability and an increased number of sick leave days compared with those without cough. This pattern was consistent after adjusting for age, BMI, education level, smoking status and comorbidities. Reporting chronic cough at baseline was independently associated with lower work ability and an increased number of sick leave days 10 years later.
Prevalence and development of chronic cough
To date, the prevalence of chronic cough has varied significantly between epidemiological studies. This may stem from differing definitions of chronic cough, and differences between study populations and regions [5]. A meta-analysis found the overall global prevalence to be 9.6% (95% CI 7.6–11.7%) and that in Europe to be 12.7% (95% CI 10.4–15.2%) [5]. Our prevalence is somewhat higher. This could be due to the fact that in the present study the definition of chronic cough lacks a specific timeframe, only that the cough is protracted and troublesome. Also, it does not encompass if the cough is troublesome on a daily basis and therefore might not be representative of the patient population seen in clinical practice. Another notable aspect is that many of these studies do not differentiate between productive and nonproductive cough, which also may affect the results. There is a need for more standardised questionnaires on chronic cough, to facilitate further epidemiological and clinical studies of this condition.
Several differences were seen between individuals with nonproductive cough and those with productive cough, even though the definition was based on self-reported symptoms without objective validation. Nonproductive cough was more associated with female sex, while productive cough was more associated with a smoking history, higher BMI, lower education level and respiratory comorbidity. These demographic differences underscore that these two types of cough seem to represent different clinical cohorts and indeed they also differed in reported comorbidities. Participants with nonproductive cough had mostly reflux and/or asthma, whereas those with productive cough had mostly rhinitis and/or asthma, and COPD was much more common than in nonproductive cough. Overall, those with productive cough more often had a possible identifiable cause for their cough.
We found a small nonsignificant increase in prevalence of both productive and nonproductive cough over a 10-year period. One-third of the participants with nonproductive cough and half of the participants with productive cough at baseline also reported chronic cough at follow-up. A considerable proportion of participants reported a change in cough character over time, where nonproductive cough more often changed to productive cough than vice versa. Previous studies on the natural history of chronic cough are scarce. In a longitudinal study on patients with idiopathic chronic cough attending a specialist cough clinic (n=42), 60% had unchanged or worsened cough 7 years later [7]. Koskela et al. [8] reported that among patients with chronic cough (n=68), roughly one in two had a persistent cough after a 5-year follow-up period. Our results from a large general population cohort confirm that cough seems to persist over time in a substantial proportion of subjects.
Work ability and sick leave days
Apart from causing increased levels of morbidity in the community, chronic cough also causes a high rate of healthcare utilisation [24]. In the present study, we found participants with chronic cough less often reported high work ability compared with those without cough. Work ability has also been studied in asthma. Compared with a Norwegian general population study on asthma and work ability, using the same question as in our study [25], our results show a somewhat stronger impact of chronic cough on work ability. We found that 49% of participants with current asthma reported excellent work ability, which is similar to the rate among those with chronic nonproductive cough, but higher than among those with productive cough. Thus, chronic cough seems to have a significant impact on work ability in the general population, to a similar or higher degree than asthma.
We also found chronic cough to be an independent risk factor for increased sick leave days. Our results share similarities with the findings of Koskela et al. [11], that chronic cough independently associates with having >7 days sick leave in the preceding year. We are not aware of other studies on this specific association. A further indication of a significant negative effect from chronic cough was our finding of a higher frequency of change in job because of breathing problems, even after adjusting for confounding factors, including airway diseases such as asthma and COPD.
Some notable differences were found between males and females with chronic nonproductive cough. Our results suggested that in this cough group, males experience themselves less efficient at work than females, even though males were less likely to take sick leave days than females. Fewer sex-based differences were seen for those with productive cough. The reason for this difference is not entirely clear.
A large study from the USA found asthma to associate with a modest increase in sick leave (25 versus 24 absence days for asthmatic versus nonasthmatic subjects, respectively) [26]. A general population study from Denmark found sick leave weeks to be ∼40% more common among asthmatic than nonasthmatic subjects [27]. A Norwegian general population study found a somewhat lower difference in sick leave between asthmatic and nonasthmatic subjects [25].
Taken together, our data suggest that a reported chronic cough may have at least an equal impact on sick leave days as asthma in the general population. Additionally, we found the association between chronic cough and sick leave days to be similar among asthmatic and nonasthmatic subjects. Therefore, we conclude that chronic cough is not merely a surrogate for asthma in this aspect, but a specific entity that needs to be addressed.
Another notable finding was that cough 10 years earlier had a predictive value for sick leave days, even among those who did not report any cough at follow-up. The highest prevalence of sick leave days was found among participants with a persistent chronic cough over 10 years. We are not aware of any previous study looking at this association over time and the cause of this effect is not entirely clear. Possibly, a previous history of chronic cough may indicate a risk for relapsing periods with prolonged coughing, which may result in more frequent sick leave. The fact that persistent chronic cough associates with more sick leave than intermittent chronic cough indicates a need to address chronic cough early and effectively to minimise further sick leave.
Strengths and limitations
The main strength of this study lies in the large general population cohort from multiple study centres, with a long follow-up, which makes the results applicable to the Northern European general population. However, some methodological limitations also need to be addressed. First, our definition of chronic cough was not based on having symptoms for a specified period of time, possibly resulting in some misclassification. This may explain why our prevalence is higher than in some, but not all, previous epidemiological studies. A wider definition would arguably lead to weaker associations; however, our findings still show a significant impact even with this wide definition.
Second, we did not use a full, validated questionnaire to assess work ability, such as the WAI. However, the questions used have been shown to reflect such questionnaires adequately [21, 28]. We did not have data on sick leave and work ability at baseline. We also did not have objective data, such as registry data on sick leave days, to validate the self-reported sick leave days.
Third, the dropout from the original RHINE cohort may have caused a nonresponse bias. This possibility has been studied specifically and the risk for bias found to be minimal [15]. It is therefore unlikely that our results are influenced by nonresponse bias.
Conclusions
Chronic cough is common in the adult general population, and population characteristics such as smoking history, BMI and education level differ between participants with nonproductive cough and those with productive cough. Both types of chronic cough associate with more sick leave from work and also associate with increased sick leave 10 years later in life. Our findings indicate significant negative effects on employment from chronic cough in the general population that needs to be addressed in further studies on chronic cough, including interventional studies.
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Supplementary Material
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Acknowledgements
We thank the Statistical Consulting Center at the University of Iceland (Reykjavik, Iceland) for advice on the statistical analysis.
Footnotes
Author contributions: H. Johansson, Ö.I. Emilsson, A. Malinovschi and A. Johannessen contributed significantly to the conception of this study. Ö.I. Emilsson performed the statistical analysis. All authors participated in discussions for the development of the study and contributed to the data interpretation. All authors read, contributed to and approved the final manuscript.
Conflict of interest: A. Johannessen has nothing to disclose.
Conflict of interest: M. Holm has nothing to disclose.
Conflict of interest: B. Forsberg has nothing to disclose.
Conflict of interest: V. Schlünssen has nothing to disclose.
Conflict of interest: R. Jõgi has nothing to disclose.
Conflict of interest: M. Clausen has nothing to disclose.
Conflict of interest: E. Lindberg has nothing to disclose.
Conflict of interest: A. Malinovschi has nothing to disclose.
Conflict of interest: Ö.I. Emilsson has nothing to disclose.
Conflict of interest: H. Johansson has nothing to disclose.
Support statement: RHINE was supported financially by the Norwegian Research Council, Bergen Medical Research Foundation, Western Norwegian Regional Health Authorities, Norwegian Labour Inspection, Norwegian Asthma and Allergy Association, Faculty of Health of Aarhus University, Wood Dust Foundation, Danish Lung Association, Swedish Heart and Lung Foundation, Vårdal Foundation for Health Care Science and Allergy Research, Swedish Council for Working Life and Social Research, Bror Hjerpstedt Foundation, Swedish Asthma and Allergy Association, Icelandic Research Council, and Estonian Science Foundation. Funding information for this article has been deposited with the Crossref Funder Registry.
- Received September 1, 2020.
- Accepted November 12, 2020.
- Copyright ©ERS 2021
References
