The impacts of cough: a cross-sectional study in a Finnish adult employee population

Discussion

The present community-based study among working-age, employed subjects revealed that in spite of the negative impacts of cough on QoL, it is not associated with depressive symptoms. Furthermore, cough substantially increases doctor's visits and sick leave days. The impacts of acute cough were smaller than the longer cough subtypes while the impacts of subacute and chronic cough were comparable.

In the present unselected cough population, the mean LCQ total score was 15.2 among subjects with cough of any duration and 14.6 among subjects with chronic cough. To our knowledge, there is only one previous community-based study utilising the LCQ reporting a mean total score of 17.3 among Danish subjects with chronic cough [11]. The rather low response rate may, at least partly, explain the worse QoL in the present population. Perhaps the subjects with severe cough were more willing to participate than subjects with mild cough. However, the LCQ total scores are usually still much lower in the populations from specialised cough clinics, with mean or median values of 12–13 [12–14]. These findings indicate that subjects attending such clinics probably represent highly selected, very disabled cough subjects and that findings among such populations may not be applicable to the cough population in community.

The present study is, to our knowledge, the first to compare LCQ scores between acute, subacute and chronic cough. It revealed that acute cough has lesser impact on QoL than the longer cough subtypes whereas there were no differences between subacute and chronic cough. It has been shown before that cough-related QoL is strongly related to objectively counted cough frequency during ambulatory recording [12]. In the present study, self-assessed cough bout frequency was lower in acute cough than in the longer cough subtypes, which may partly explain the differences in QoL. Furthermore, LCQ was originally developed for chronic cough. There is an “acute” version of it in which each item relates to the patient's experience within a 24-h time frame, in contrast to the 2-weeks time frame in the traditional LCQ [15]. However, it was impossible to use two different QoL instruments in the present type of study.

One previous community-based study [4] and two previous studies from specialised cough clinics [16, 17] suggested that chronic cough might be associated with depressive symptoms. On the contrary, in the present population, the prevalence of depressive symptoms was 5.0% among subjects without any cough and 4.8% among subjects with chronic cough. There are obvious reasons for this discrepancy. In the previous community-based study, a validated depressive symptom questionnaire was not used and the prevalence figures were not compared to those in healthy subjects [4]. The populations in the specialised cough clinics probably represent highly selected, very disabled cough subjects, as mentioned before. The population in the present study was unselected, a comparison with healthy subjects was performed and a well-validated depressive symptom questionnaire was utilised. In the present study, we could not diagnose clinical depression but measured the depressive symptoms. However, utilising the cut-off value ≥3, PHQ-2 has a sensitivity of 83% and specificity of 92% for clinically confirmed major depression [10]. Of note, in a previous Finnish community-based study with >6000 mental health interviews the prevalence of major depression was 4.9%, i.e. almost identical to the prevalence of depressive symptoms in the present population, supporting the reliability of PHQ-2 [18].

As expected, current cough was often associated with doctor's visits [4, 19, 20]. In previous community-based surveys, 91–93% of subjects with chronic cough had visited a doctor at least once [4, 20]. In the present study, 41.6% of the subjects with chronic cough had visited a doctor at least once due to current cough. Though this is a high percentage, it is considerably lower than that in the previous studies. Very probably, the previous studies suffer from a significant reporting bias associated with the nonsystematic recruitment of the populations [4, 20].

Chronic cough was associated with larger number of doctor's visits due to current cough than both subacute and acute cough. However, when the doctor's visits were analysed within a period of 12 months, the difference between subacute and chronic cough vanished. There may be two explanations for this. First, in the majority of chronic cough subjects, the cough had lasted >1 year. In these subjects, the number of doctor's visits due to cough per one year can be smaller than that due to current cough. Second, there may be several episodes of subacute cough per 1 year. We have shown previously that subacute cough is associated with chronic rhinosinusitis and asthma [21]. These disorders are often episodic, activated by seasonal allergens or upper respiratory tract infections and these episodes can take place several times a year. Thus, within certain time limits, like 1 year, recurrent subacute cough may cause as many doctor's visits as chronic cough. Acute cough seems to prompt doctor's visits less often than the two longer cough subtypes.

Cough also increased the probability of doctor's visits due to any reason. In the model containing several confounders that could explain frequent doctor's visits, current cough independently increased the probability of such a visit by 36% within 1 year and the probability of frequent (≥3) visits by 49%. These figures can be regarded as highly significant with respect to health resource utilisation. Again, this impact was mainly associated with subacute and chronic cough.

Sick leave days due to cough are difficult to investigate. In Finland, a symptom is not a legitimate ground for a sick leave day. Therefore, diagnoses like “bronchitis” are used in health certificates. In the present study, the subjects were asked to subjectively estimate how many sick leave days took place due to cough. Unfortunately, the questionnaire did not include a question about sick leave days due to current cough. However, the sick leave days within the last 12 months were sought, both due to cough and due to any reasons. Strikingly, current cough independently increased the risk of a sick leave day due to any reason by 60%, corroborating the large socioeconomic burden of cough. The model showing this included several confounders that could be associated with sick leave days, like age, sex, body mass index, sum symptom score, depressive symptoms and family incomes. The sum symptom score is an important confounder which probably represents somatisation. It describes the interindividual variation in how subjects recognise and report symptoms [22]. Again, subacute and chronic cough increased the sick leave days more than acute cough.

It seems that acute cough induces fewer doctor's visits and sick leave days than prolonged cough. One obvious reason for this is the lower cough frequency and less impaired QoL in acute cough. In addition, people probably are often aware of the self-limiting nature of acute cough or acute bronchitis and may regard a doctor's visit unnecessary. Furthermore, in many workplaces in Finland, an employee is entitled to ≤5 days absenteeism even without a health certificate by a doctor. The latter facts may partly explain the relatively low number of doctor's visits in acute cough but not the relatively low number of sick leave days.

The three most commonly recognised chronic cough background disorders (chronic rhinosinusitis, asthma and gastro-oesophageal reflux disease) [23, 24] were included in the analyses as possible confounders. However, they were associated neither with the doctor's visits nor the sick leave days. These findings suggest that it is the cough itself, not the background disease, that mainly defines the impacts. This supports the rationale of cough hypersensitivity syndrome, a conception that long-standing hypersensitivity of cough reflex arch is an independent disorder [25, 26].

There are several shortcomings in the present study. All of the information used in the present analyses were based on self-reports in a cross-sectional design with the associated problems of biased reporting and lack of possibility to separate associations from causality. The participation rate was relatively low. It is possible that subjects with current cough were more interested to participate than those without. However, the responders and nonresponders did not differ with respect to age or sex distribution. The low participation rate probably affects more the cough prevalence values than the impact analyses. The generalisability of the study may be limited since the subjects were public service employees. Low social classes and old persons are therefore underrepresented. However, this population is very suitable to analyse doctor's visits and sick leave days because as public service employees, they are provided with a free health service and an equal, easy access to doctors. The impacts would probably have been greater if certain bout frequency criteria (e.g. daily cough) were utilised. However, we wanted an unselected cough population.

In conclusion, the present study shows that cough affects QoL and causes a substantial socioeconomic burden by increasing the probability of doctor's visits and sick leave days. However, it is not associated with depressive symptoms, not even chronic cough. The impacts of subacute and chronic cough are comparable, and larger than those of acute cough. Given the fact that the risk factors for subacute and chronic cough are very similar [21], it may be unnecessary to divide prolonged (>3 weeks) cough to two subclasses. Focusing on the characteristics of a single cough episode may sometimes be misleading and more attention should be paid on the recurrence of cough episodes, even if they are short.