What good came out of the Covid-19 outbreak for workers with occupational asthma?

KEYWORDS:

• Covid-19
• lung function
• occupational asthma

1. Background

Occupational asthma accounts for about 15% of adult-onset asthma [1] and is associated with poorer quality of life than in workers with similar asthma severity not caused by exposures at work, mainly because of the loss of income and chances of promotion when work is the cause of the disease [2,3]. Every adult with asthma should have a search for remedial triggers of which occupation is one of the most important. The standard screening questions are for symptom improvement on days away from work or on holiday [4] as the onset of symptoms after exposure is often delayed for several hours after exposure starts, and is superimposed on the normal diurnal variation in airflow obstruction which has a nadir around waking and an acrophase (the best) around 6–12 hours after waking. This means that any effect of dayshift working is superimposed on the spontaneous improving phase of airflow limitation, often resulting in occupational asthma being worse after work rather than during work exposures, hence asking for rest-day improvement rather than worse at work [5]. Much less is known about continued week-by-week or year-by-year exposures in sensitized workers. Catastrophic asthma attacks due to occupational exposures are rare, and are most common in sensitized workers who have been removed from exposure for some time and then usually inadvertently exposed to the sensitizing agent at levels causing no effect in non-sensitized workers. There is however evidence of accelerated loss of FEV₁ in sensitized workers with continued exposure to the cause [6]. In some this may result in what appears to be fixed airflow obstruction resembling COPD rather than asthma. Such workers may not show weekend symptom improvement, and may not even show improvement on holidays. The question on holiday improvement usually entails removal from exposures associated with the home and home environment, making it less specific for occupational asthma.

2. Impact of Covid-19 pandemic

The first Covid-19 lockdown resulted in the closure of most non-essential manufacturing and home working for those who could, nearly always for more than 4 weeks and often much longer. This allowed time for asthma improvement in the difficult group who had been missed by lack of rest-day and holiday improvement.

1. 1 On the downside most surveillance lung function at work, and most hospital-based lung function laboratories, stopped working as lung function testing was classified as aerosol generating [7,8], requiring increased personal protection for the physiologists, increased ventilation for the spirometry room, increased time between those being tested (sometimes several hours for naturally ventilated rooms), although aerosol generation from Covid-19 positive patients has not been supported by public health authorities [9].

2. 2 Managing chronic respiratory disease without lung function transfers an evidence-based approach to treatment with guesswork, opening the way for remote spirometry testing. Reasonably priced hand-held single patient meters and reusable meters (able to be disinfected) are now available measuring peak flow, FEV₁ and sometimes FVC and flow-volume loops. Measurements can be made successfully unsupervised by patients who have been trained face-to-face (most suitable for those making daily measurements) [10], or remotely supervised via video links to a trained physiology technician or scientist, more suitable for those making measurements less frequently. Currently development software is available from magic bullet and links to the Vitalograph Lung Monitor BT 4000 (FEV₁ and FVC₆) and MIR Spirobank Smart (flow-volume loop), publications on the relationship between laboratory and measurements at home are awaited. Others have developed in-car drive through spirometry, supervised by a physiologist outside the car [11].

3. 3 Spirometry is required for measurement of longitudinal decline in FEV₁, important in monitoring over short periods of time for lung transplant patients [12] or moderate periods for patients with rapidly progressive interstitial pulmonary fibrosis [10], or annually for surveillance of workers exposed to respiratory sensitizers and COPD promoting exposures such as silica [13].

3. Pear flow monitoring in the diagnosis of occupational asthma

Peak Expiratory Flow (PEF) has advantages in the diagnosis of occupational asthma from the Oasys analysis of 2-hourly measurements over several weeks [14,15]. In this situation PEF has been shown to be at least as sensitive and specific as FEV₁ [16], is cheaper and the acquisition of reliable repeatable measurements easier than with unsupervised FEV₁ measurements. The analysis of serial 2-hourly PEF measurements is the method of choice for validation of the diagnosis of occupational asthma in those with a history of work-related symptoms [17].

1. One of the unresolved issues of PEF monitoring is the interpretation of very small changes in PEF related to work exposure which are nevertheless outside the 95% confidence intervals for those with asthma unrelated to work.

Figure 1 shows the Oasys plot of mean PEF in 2-hourly blocks over 4 weeks from waking to sleeping in an office-based IT worker, working in the office (top panel) and at home (bottom panel) during the Covid-19 lockdown. We had visited her air-conditioned office twice and performed a workplace challenge without confirming a diagnosis or finding a cause. The plot red line with crosses shows the values on workdays and the blue squares for days not working. The mode times at work have heavy vertical lines and background shading, showing the earliest time of starting work (0600) and the earliest time for stopping work (1200 upper panel, 1600 lower panel) and the latest time for stopping work (1800 lower panel). Below the time panel are the number of days readings contributing to each data point (working days in red on the left and non-working days in blue on the right). Below this is the Area Between Curves (ABC) difference for each 2-hourly data point, with the mean ABC score at the bottom (minus 2 and minus 7 litres/min, showing that the mean PEF was higher on workdays). However there is one time point in the top panel between 1830 and 2030 when the mean workday PEF is below the 95% CI for non-work days, the differences is very small (15 litres/min) making interpretation difficult. Single non-waking positive timepoints as in the top panel have a sensitivity of 77% and specificity of 93% in an individual using specific challenge positive asthmatics as positive controls and asthmatic without occupational asthma as negative controls [18].

Figure 1. Shows the Oasys plot of mean PEF in 2-hourly blocks over 4 weeks from waking to sleeping in an office-based IT worker, working in the office (top panel) and at home (bottom panel) during the Covid-19 lockdown. We had visited her air-conditioned office twice and performed a workplace challenge without confirming a diagnosis or finding a cause. The plot red line with crosses shows the values on workdays and the blue squares for days not working. The mode times at work have heavy vertical lines and background shading, showing the earliest time of starting work (0600) and the earliest time for stopping work (1200 upper panel, 1600 lower panel) and the latest time for stopping work (1800 lower panel). Below the time panel are the number of days readings contributing to each data point (working days in red on the left and non-working days in blue on the right). Below this is the area between curves (ABC) difference for each 2-hourly data point, with the mean ABC score at the bottom (minus 2 and minus 7 litres/min, showing that the mean PEF was higher on workdays). However there is one time point in the top panel between 1830 and 2030 when the mean workday PEF is below the 95% CI for non-work days, the differences is very small (15 litres/min) making interpretation difficult. Single non-waking positive timepoints as in the top panel have a sensitivity of 77% and specificity of 93% in an individual using specific challenge positive asthmatics as positive controls and asthmatic without occupational asthma as negative controls [18]

1. Changes in PEF are not however specific for asthma. PEF is dependant on vital capacity and is reduced in restrictive disease. If the restrictive disease shows changes over hours or days, as in some patients with hypersensitivity pneumonitis, serial measurements of PEF may be able to detect an occupational cause [19], and are also seen in workers with occupational inducible laryngeal obstruction [20,21]. There was however no evidence of hypersensitivity pneumonitis or laryngeal obstruction in this worker. The positive time-point at the same time of day was repeated in a second 4-week record, making a random effect very unlikely. The bottom panel shows that the significant timepoint is no longer present when working at home, and the mean PEFs are about 50 litres/min higher, confirming the diagnosis of occupational asthma, only possible because of paid long-term removal from her usual workplace during the Covid-19 outbreak. At least one positive outcome from this dreadful disease.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This paper was not funded.