Fear of COVID-19 Among Japanese Workers and Exacerbation of Chronic Pain

A Nationwide Cross-Sectional Study

Abstract

Objective 

To evaluate the association between fear of the coronavirus disease 2019 (COVID-19) and exacerbated chronic pain among workers during the pandemic, as well as productivity loss.

Methods 

We collected data using Internet-based self-reported questionnaires, on fear of COVID-19, work productivity status, exacerbation of chronic pain during the pandemic, and several confounding factors.

Results 

The multivariate logistic regression analysis showed that a high level of fear of COVID-19 was associated with an increased exacerbation of chronic pain (adjusted odds ratio, 2.31; 95% confidence interval, 1.21–4.44). Meanwhile, the presence of fear of COVID-19 and exacerbated chronic pain were associated with productivity impairment (adjusted odds ratio, 2.03; 95% confidence interval, 1.44–2.85).

Conclusions 

Our study shows that workers' fear of COVID-19 is correlated with exacerbated chronic pain and risk of presenteeism.

In Brief

Our results revealed that workers’ fear of COVID-19 was correlated with exacerbated chronic pain during the pandemic and lead to reduced labor productivity; our study highlights the need for effective interventions to provide workers with the appropriate education and information to help minimize their fear of COVID-19.

LEARNING OUTCOMES

• Upon completion of this learning activity, participants should be able to realize that workers' fear of COVID-19 leads to reduced labor productivity.
• The concept that participants learn is that nociplastic pain is expressed as the exacerbation of chronic pain. This understanding will help them learn about the negative aspects of the fear of COVID-19 and create the ground for discussion on how workers' fear of COVID-19 can be reduced by providing appropriate education and information.

Various types of chronic pain affect approximately 20% of the world's population.¹ In 2019, the International Association for the Study of Pain classified chronic pain into chronic primary and secondary pain. Chronic secondary pain is caused by an underlying disorder or tissue damage. There are many different types of underlying disorders that may cause chronic pain, such as cancer, neuropathic pain, osteoarthritis, and Parkinson's disease. Chronic primary pain refers to hypersensitivity to pain, even though nociceptor activation or neuropathy due to tissue damage or inflammation is not observed. Biological, psychological, and social factors are believed to be intricately associated with chronic primary pain. Chronic primary pain also includes nonspecific chronic lower back pain that is not classified as musculoskeletal or neuropathic, and so-called functional visceral pain, such as irritable bowel syndrome.^2,3 Some types of chronic primary pain are considered to be nociplastic pain.² Nociplastic pain is defined as pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage that would cause the activation of peripheral nociceptors, or evidence of disease or lesion of the somatosensory system that would cause pain, and is one of the contributing factors to chronic pain.⁴

The concept of presenteeism has been used to define the phenomenon of individuals who attend work despite illness or despite having some kind of poor condition, instead of taking time off work to rest and recover.⁵ Some health conditions, such as chronic pain, heart disease, diabetes, allergies, depression, and other mental health problems, are also known to increase the risk of presenteeism.^6,7 Chronic pain, such as neck and shoulder pain, back pain, and headaches, has been found to cause worker presenteeism and to increase the loss of labor productivity.^8,9 Hidden economic losses in work productivity due to disease are greater than the medical expenses directly incurred as a result of the illness. The impact of presenteeism on such losses is twice or thrice more than that of absenteeism,¹⁰ and thus presenteeism has received much attention in recent years.

On April 7, 2020, the Japanese government declared a state of emergency to prevent the spread of the coronavirus disease 2019 (COVID-19) in the capital and metropolitan areas. This was expanded to the entire nation on April 16, 2020. Although it was a noncompulsory measure, public behavioral changes, including avoiding crowds, the closure of nonessential businesses, staying at home and other movement restrictions were strongly encouraged. These measures reduced human movement.¹¹ Worldwide, the COVID-19 pandemic has negatively affected the physical, psychosocial, and socioeconomic aspects of many individuals' lives, including workers.^12–14 Individuals face psychological stress caused by fear and anxiety due to the high transmission and mortality rates of the disease, as well as unemployment and economic difficulties caused by the pandemic.^15,16

A recent study has indicated that patients with fibromyalgia, which has been classified as chronic primary pain in the latest edition of the World Health Organization's International Classification of Diseases 11th Revision, had a higher level of fear of COVID-19 than the control group (nonpain), and the level of fear correlated with the severity of fibromyalgia symptoms.¹⁷ People who experience chronic pain besides those with fibromyalgia may also have a strong fear of COVID-19 and their pain may also be exacerbated. Meanwhile, few studies have investigated the relationship between workers' level of fear of COVID-19 and worsening chronic pain during the COVID-19 pandemic. Thus, we hypothesized that during the pandemic, especially among workers with a high level of fear of COVID-19, this may correlate with presenteeism, including the exacerbation of chronic pain. The primary purpose of this study was to clarify whether fear of COVID-19 is associated with the worsening of chronic pain in workers. Our second aim was to assess the relationship between fear of COVID-19 and productivity impairment because of presenteeism and the exacerbation of chronic pain.

METHODS

Study Design, Setting, and Data Sources

We analyzed data collected in the Japan “COVID-19 and Society” Internet Survey study, which was a cross-sectional, Internet-based, self-reported questionnaire survey administered by a large Internet research agency, Rakuten Insight Inc. A random sampling method was used to recruit participants for our study using a computer algorithm. The sample was representative of the official demographic composition of Japan as of October 1, 2019, based on categories, such as age, sex, and geographical area of residence (i.e., prefecture). The participants who consented to participate in the survey accessed the designated website and responded to the items contained in the questionnaires. The participants were made aware that they had the option of not responding to any of the questions or of withdrawing from the study at any point in the survey. We started to distribute the questionnaires on August 25, 2020, and distribution was completed on September 30, 2020, when the number of participants met the target numbers for each sex, age, and prefecture category, which had been determined in advance according to the population distribution in 2019. The ethics committee at Osaka International Cancer Institute approved the study protocol (approval number: 20084).

Study Population

We distributed questionnaires until the number of respondents reached the target sample size (n = 28,000, response rate = 12.5%). We defined invalid responses as follows: respondents who, when asked to select the second item from the bottom of a list in our dummy question, failed to do so (n = 1955); respondents who chose every item in a list of seven substances (alcohol, sleeping medications, opioids, sniffing paint thinner, legal-high drugs, marijuana, and cocaine/heroin) (n = 422); and respondents who chose every item in a list of 16 diseases (n = 141, refer to the disease name in the Demographic factors section). We excluded 10,028 respondents who reported that they were currently unemployed and 2518 respondents who provided unreliable responses. From the responses of 15,454 respondents, only those of 2475 respondents who were currently working and who had experienced chronic pain were eligible for inclusion in our study (Fig. 1).

FIGURE 1: Flowchart of this study participants.

Chronic Pain

Participants were questioned regarding their experience of chronic pain and whether they had experienced it for a period of 3 months or more. They could choose from one of four responses as follows: “none,” “I have a history of chronic pain, but have already recovered,” “yes, I am receiving treatment,” or “yes, I am not receiving treatment.” We considered answers other than “none” to indicate a history of chronic pain. Regarding the exacerbation of chronic pain during the COVID-19 pandemic, we asked the participants if their chronic pain “got worse during the period of April to May 2020 when there was a state of emergency declared.” The participants could choose either “yes” or “no” as a response. We concluded that the participants’ chronic pain had worsened if they answered “yes” to this question. The questions did not include the site of chronic pain, the duration and intensity of the pain, and the name of the disease causing the pain.

Fear of COVID-19 Scale

The Fear of COVID-19 scale (FCV-19S) is a short questionnaire developed to evaluate the levels of fear and anxiety related to COVID-19. Originally developed in Persian,¹⁸ it has been validated in various languages.^19–22 In Japan, three studies have validated it.^23–25 The scale consists of seven statements: (1) My heart races or palpitates when I think about getting coronavirus-19. (2) I cannot sleep because I'm worrying about getting coronavirus-19. (3) My hands become clammy when I think about coronavirus-19. (4) When watching news and stories about coronavirus-19 on social media, I become nervous or anxious. (5) It makes me uncomfortable to think about coronavirus-19. (6) I am most afraid of coronavirus-19. (7) I am afraid of losing my life because of coronavirus-19. Each item is evaluated on a five-point Likert scale (1, strongly disagree to 5, strongly agree). The total score is calculated by adding up each item's score to obtain a range of 7 to 35. The higher the score, the greater the individual's fear of contracting COVID-19.

The cutoff value for FCV-19S in our study was 16.5.²⁶ However, to our knowledge, no studies have defined the severity of fear and anxiety levels related to COVID-19 (e.g., minor, moderate, and major), and there is no formal standardized cutoff value for severity in the FCV-19S. Thus, we divided fear scores into three levels of severity: “minor,” “moderate,” and “major” based on the values obtained by dividing the scores over 17 points and under 35 points into three equal parts (no fear, <17; minor, 17–22; moderate, 23–28; major, 29–35). Participants were asked to respond to questions on the FCV-19s regarding their feelings at the time of answering (August–September 2020).

Evaluation of Productivity Loss Due to Presenteeism Using the Work Functioning Impairment Scale

The seven-item Work Functioning Impairment Scale (WFun) was developed in Japan and has shown good correlation with measures of different types of presenteeism proposed by scholars in recent years.²⁷ It is also one of the simplest measures of productivity loss due to presenteeism.²⁸ The WFun measures individuals' ability to function at work by having them respond to the following statements: (1) I have not been able to behave socially, (2) I have not been able to maintain the quality of my work, (3) I have had trouble thinking clearly, (4) I have taken more breaks during my work, (5) I have felt that my work is not going well, (6) I have not been able to make rational decisions, and (7) I have not been proactive about my work. The participants had a choice of the following five responses: “not at all,” “about 1 day a month,” “about 1 day a week,” “two or more days a week,” and “almost every day.” The participants' overall score was calculated by adding the scores of the seven items, and the scores ranged from 7 to 35 points. A higher score means worse work impairment, and 21 points or more can be judged as severe work impairment.²⁹ Participants were asked to respond to questions on the WFun regarding the situation at the time of answering (August–September 2020).

Demographic Factors

The demographic factors assessed included age, sex, and health-related variables, such as the existence of preexisting diseases (such as hypertension, diabetes, asthma, bronchitis and pneumonia, atopic dermatitis, periodontal disease, caries/tooth decay, otitis media, angina pectoris, myocardial infarction, chronic obstructive pulmonary disease, cancer and malignancies, depression, or psychiatric disorders other than depression and stroke).

Socioeconomic Factors

Several work environment factors were also evaluated. These included the type of job, namely blue-collar, desk work, and other, which mainly comprised “pink-collar” jobs, such as customer service, retail, and nursing care work,³⁰ and employment status, which was divided into three categories: regular employee (company executive and management/nonmanagement level employee), nonregular employee (contracted term employee, part-time employee, and work from home employee) and family-operated business. We also collected data on the participants' level of education.

Socioeconomic status was evaluated by household income in 2019 and change in household income after the pandemic in 2020. The change in household income was evaluated using the following question: “Having your previous household income as 100, how has your current household income changed? For example, answer 50 if it has been reduced by half or answer 200 if it has doubled.” The participants either provided a number or chose the option “do not know.” The variables were categorized into four groups as follows: “reduced,” “did not change,” “increased,” and “do not know.” The impact of the COVID-19 pandemic on socioeconomic conditions was assessed in terms of work-related physical burden. Information on work-related physical burden was gathered by asking the participants the following multiple-choice question: “Since April 2020, have you had any of the following experiences due to the COVID-19 pandemic? Has the physical burden of your work increased?” The participants had a choice of three responses: “yes,” “no,” or “not applicable.”

In this study, to consider the influence of epidemic/nonepidemic areas under the declaration of a state of emergency from April to May 2020, 13 prefectures that were classified as specific caution prefectures were considered to be infections epidemic areas. These were as follows: Hokkaido, Ibaragi, Saitama, Tiba, Tokyo, Kanagawa, Ishikawa, Gifu, Aichi, Kyoto, Osaka, Hyogo, and Fukuoka. Thirty-four areas other than the 13 mentioned above were classified as nonepidemic areas (Japan consists of 47 prefectures in total).

Statistical Analyses

Data analyses were conducted using JMP version 14.0.0 (SAS Institute Inc., Cary, NC). Multivariable logistic regression models were used to analyze the association between exacerbation of chronic pain during the pandemic and the level of fear of COVID-19 scale, adjusted for sex, age, under treatment for chronic pain, number of preexisting diseases, psychiatric disorders, job type, employment status, household annual income in 2019, change in household income, epidemic status of residence, and increase in physical burden at work after April 2020. In addition, the same statistical techniques were used to evaluate the association between the level of COVID-19 fear and the WFun score. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) derived from the models were reported, all P values were two-sided, and P < 0.05 was considered statistically significant.

RESULTS

Frequency of Worsened Chronic Pain, Fear of COVID-19, and Work Impairment

The characteristics of the participants included in the present study are summarized and presented in Table 1. Of the 2475 participants, half of them were male (54.4%) and were desk workers (44.3%). The percentages of younger age group (25.5%) and older age group (22.9%) were almost the same. Approximately 60% of the participants lived in epidemic areas. Approximately 7.5% (n = 185) of the participants experienced worsened chronic pain during the state of emergency. Regarding levels of fear of COVID-19 experienced by the participants, 38.7% reported feeling no fear, while 40.3% experienced a minor level of fear. Approximately 17% experienced a moderate level of fear, whereas 4% reported feeling a major level of fear. Nearly one quarter of the participants (24.5%) scored 21 points or more on the WFun scale, indicating severe work impairment.

TABLE 1 - Demographic Characteristics of the Participants by Chronic Pain Change Status During a State of Emergency

	Total (Experienced With Chronic Pain)		Without Worsened Chronic Pain		With Worsened Chronic Pain
	N = 2475 (100.0%)	%	n = 2290 (92.5%)	%	n = 185 (7.5%)	%
Sex
Male	1347	54.4	1250	54.6	97	52.4
Female	1128	45.6	1040	45.4	88	47.6
Age (in yrs)
≤39	632	25.5	568	24.8	64	34.6
40 to 59	1277	51.6	1177	51.4	100	54.1
≥60	566	22.9	545	23.8	21	11.3
Receiving treatment for chronic pain
Yes	543	21.9	479	20.9	64	34.6
Diagnosed with depression, or psychiatric disorders other than depression/receiving treatment for depression or other psychiatric disorders
Presence	308	12.4	240	10.5	68	(36.8)
Preexisting diseases, a excluding depression and other psychiatric disorders
0	1136	45.9	1065	46.5	71	(38.4)
1	669	27.0	622	27.1	47	(25.4)
≥2	670	27.1	603	26.4	67	(36.2)
Fear of COVID-19 Scale (7–35)
7–16: no fear	957	38.7	899	39.2	58	31.3
17–22: minor	997	40.3	928	40.5	69	37.3
23–28: moderate	423	17.0	384	16.8	39	21.1
29–35: major	98	4.0	79	3.5	19	10.3
Educational attainment
College or higher	1168	47.2	1074	46.9	94	50.8
Vocational/Technical school	617	24.9	573	25.0	44	23.8
High school or lower	690	27.9	643	28.1	47	25.4
Job type
Blue-collar worker	765	30.9	724	31.6	41	22.2
Desk worker	1096	44.3	1008	44.0	88	47.6
Other	614	24.8	558	24.4	56	30.2
Employment status
Regular employee	1365	55.2	1263	55.2	102	55.1
Nonregular employee	807	32.6	745	32.5	62	33.5
Family-operated business	303	12.2	282	12.3	21	11.4
Household annual income in 2019 (thousand Japanese Yen)
≥6000	904	36.5	840	36.7	64	34.6
3000–5999	801	32.4	744	32.5	57	30.8
0–2999	403	16.3	365	15.9	38	20.5
Do not want to answer	202	8.2	186	8.1	16	8.6
Do not know	165	6.6	155	6.8	10	5.5
Household income change
Did not change	1028	41.5	971	42.4	57	30.8
Reduced	863	34.9	783	34.2	80	43.2
Increased	106	4.3	93	4.1	13	7.1
Do not know	478	19.3	443	19.3	35	18.9
Area of residence
Epidemic area	1482	59.9	1360	59.4	122	66.0
Nonepidemic area	993	40.1	930	40.6	63	34.0
Physical burden at work after April 2020, compared with before
Increased	727	29.4	620	27.1	107	57.8
No increased	1748	70.6	1670	72.9	78	42.2
Work reduction due to the influence of COVID-19 from April 2020 to the time of answer b
Yes	917	37.1	827	36.1	90	48.6
Leave of absence due to the influence of COVID-19 from April 2020 to the time of answer b
Yes	386	15.6	331	14.4	55	29.7
Job change due to the influence of COVID-19 from April 2020 to the time of answer b
Yes	61	2.5	43	1.9	18	9.7
Work Functioning Impairment Scale
≥21 (severe work impairment)	607	24.5	517	22.6	90	48.6

^a Preexisting disease: hypertension, diabetes, asthma, bronchitis and pneumonia, atopic dermatitis, periodontal disease, caries/tooth decay, otitis media, angina pectoris, myocardial infarction, stroke, chronic obstructive pulmonary disease, cancer, and malignancies.

^b At time of answer: August 25, 2020 to September 30, 2022.

Characteristics Associated With Exacerbation of Chronic Pain

Table 2 presents the association between the level of fear of COVID-19 and exacerbation of chronic pain during the state of emergency. Fear of COVID-19 was strongly associated with an increased likelihood of exacerbation of chronic pain in both the univariable and the adjusted model: major level fear (adjusted OR [aOR], 2.31; 95% CI, 1.21–4.44). Exacerbation of chronic pain was also associated with some health-related variables: undertreatment for chronic pain (aOR, 1.75; 95% CI, 1.23–2.47), presence of psychiatric disorders (aOR, 3.84; 95% CI, 2.63–5.60), and increased physical burden in the job after the declaration of emergency (aOR, 3.37; 95% CI, 2.43–4.68). However, it was not associated with the number of preexisting diseases. Moreover, living in an epidemic or nonepidemic area was not associated with worsening chronic pain. Economic status, such as annual household income and changes in annual household income, was also not associated with worsening of chronic pain. In a comparison between three groups in which the participants were arbitrarily divided by age, the younger age group was associated with worsened chronic pain compared with the older age group 60 years or older: 40 to 59 years (aOR, 1.95; 95% CI, 1.15–3.30), 39 years or younger (aOR, 2.40; 95% CI, 1.34–4.29).

TABLE 2 - Association between the Level of Fear of COVID-19 Scale and Exacerbation of Chronic Pain

Independent variables	Dependent Variable: Worsened With Chronic Pain
	Univariable			Multivariable
	OR	95% CI	P	OR	95% CI	P
Age (in yrs)
≥60	1 (reference)			1 (reference)
40 to 59	2.20	1.36–3.57	0.001*	1.95	1.15–3.30	0.013*
≤39	2.92	1.76–4.85	<0.001*	2.40	1.34–4.29	0.003*
Fear of COVID-19 Scale
7–16: no fear	1 (reference)			1 (reference)
17–22: minor level	1.15	0.80–1.65	0.441	0.96	0.66–1.42	0.850
23–28: moderate level	1.57	1.03–2.40	0.036*	1.34	0.85–2.11	0.212
29–35: major level	3.73	2.11–6.57	<0.001*	2.31	1.21–4.44	0.012*
Receiving treatment for chronic pain
No	1 (reference)			1 (reference)
Yes	2.00	1.45–2.75	<0.001*	1.75	1.23–2.47	0.002*
Depression, or psychiatric disorders other than depression
Absence	1 (reference)			1 (reference)
Presence (current)	4.96	3.58–6.89	<0.001*	3.84	2.63–5.60	<0.001*
Preexisting diseases, a excluding depression and psychiatric disorders other than depression
0	1 (reference)			1 (reference)
1	1.13	0.77–1.66	0.520	1.14	0.76–1.72	0.532
≥2	1.67	1.18–2.32	0.004*	1.14	0.76–1.70	0.517
Physical burden at work after April 2020, compared with before
No increase	1 (reference)			1 (reference)
Increased	3.69	2.72–5.01	<0.001*	3.37	2.43–4.68	<0.001*

Covariates: sex, job type, employment status, epidemic status of residence, household income in 2019, household income change, and all variables in the table.

^a Preexisting disease: hypertension, diabetes, asthma, bronchitis and pneumonia, atopic dermatitis, periodontal disease, caries/tooth decay, otitis media, angina pectoris, myocardial infarction, stroke, chronic obstructive pulmonary disease, cancer, and malignancies.

*P < 0.05.

Characteristics Associated With Work Impairment Based on the WFun Score

Table 3 presents the association between fear of COVID-19, the presence or absence of worsened chronic pain, and the WFun score. In the univariable and multivariable analyses, participants who experienced a fear of COVID-19 or an exacerbation of chronic pain were more likely than others to show less productivity at work: minor fear (aOR, 1.54; 95% CI, 1.23–1.95), moderate fear (aOR, 1.83; 95% CI, 1.36–2.44), major fear (aOR, 2.54; 95% CI, 1.56–4.14), and the chronic pain that they experienced worsened (aOR, 2.03; 95% CI, 1.44–2.85). Health-related factors and economic factors were also associated with a high WFun score: two or more preexisting diseases (aOR, 1.34; 95% CI, 1.05–1.72), under treatment for chronic pain (aOR, 1.33; 95% CI, 1.05–1.68), presence of psychiatric disorders (aOR, 3.04; 95% CI, 2.30–4.02), and low-income household (aOR, 1.56; 95% CI, 1.14–2.12). For the younger age group, compared with the 60 years or older group, WFun ≥21 was associated with: 40 to 59 years (aOR, 2.00; 95% CI, 1.47–2.71), and 39 years or younger (aOR, 2.88; 95% CI, 2.04–4.06).

TABLE 3 - Association Among Worsened Chronic Pain, the Fear of COVID-19 Scale Level, and WFun Score

Independent variables	Dependent Variable: WFun≥21 Points
	Univariable			Multivariable
	OR	95% CI	P	OR	95% CI	P
Age (in yrs)
≥60	1 (reference)			1 (reference)
40 to 59	2.21	1.68–2.92	<0.001*	2.00	1.47–2.71	<0.001*
≤39	3.58	2.67–4.81	<0.001*	2.88	2.04–4.06	<0.001*
Fear of COVID-19 Scale
7–16: no fear	1 (reference)			1 (reference)
17–22: minor level	1.58	1.27–1.96	<0.001*	1.54	1.23–1.95	<0.001*
23–28: moderate level	1.75	1.34–2.28	<0.001*	1.83	1.36–2.44	<0.001*
29–35: major level	2.73	1.77–4.23	<0.001*	2.54	1.56–4.14	<0.001*
Chronic pain got worse during a state of emergency
No (without worsened pain)	1 (reference)			1 (reference)
Yes (with worsened pain)	3.25	2.40–0.42	<0.001*	2.03	1.44–2.85	<0.001*
Receiving treatment for chronic pain
No	1 (reference)			1 (reference)
Yes	1.56	1.26–1.92	<0.001*	1.33	1.05–1.68	0.018*
Depression, or psychiatric disorders other than depression
Absence	1 (reference)			1 (reference)
Presence	4.65	3.63–5.94	<0.001*	3.04	2.30–4.02	<0.001*
Preexisting diseasesa excluding depression and psychiatric disorders other than depression
0	1 (reference)			1 (reference)
1	1.05	0.84–1.33	0.651	1.11	0.87–1.13	0.403
≥2	1.79	1.44–2.22	<0.001*	1.34	1.05–1.72	0.020*
Household annual income in 2019 (thousand JPY)
≥6000 (high-income household)	1 (reference)			1 (reference)
3000–5999 (middle-income household)	1.10	0.88–1.37	0.393	1.12	0.88–1.43	0.348
0–2999 (low-income household)	1.34	1.03–1.75	0.029*	1.56	1.14–2.12	0.005*
Do not want to answer	0.75	0.88–1.37	0.393	0.94	0.61–1.44	0.780
Do not know	0.87	0.58–1.31	0.511	0.96	0.60–1.52	0.844
Household income change
Did not change	1 (reference)			1 (reference)
Reduced	1.50	1.21–1.86	<0.001*	1.36	1.07–1.73	0.011*
Increased	1.91	1.23–2.95	0.004*	1.39	0.86–2.25	0.175
Do not know	1.59	1.24–2.04	<0.001*	1.35	1.01–1.82	0.046*

Covariates: All variables in the table, sex, job type, employment status, and epidemic status of residence.

WFun, Work Functioning Impairment Scale.

^a Preexisting disease: hypertension, diabetes, asthma, bronchitis and pneumonia, atopic dermatitis, periodontal disease, caries/tooth decay, otitis media, angina pectoris, myocardial infarction, stroke, chronic obstructive pulmonary disease, cancer, and malignancies.

*P < 0.05.

DISCUSSION

This study evaluated the association between fear of COVID-19 and worsened chronic pain during the COVID-19 state of emergency in Japan as well as productivity loss attributed to presenteeism. To the best of our knowledge, our study is the first to provide evidence of occupational health problems associated with chronic pain that has been exacerbated by the fear of COVID-19.

We found that high levels of fear of COVID-19 were associated with exacerbation of chronic pain among workers. Our results are similar to those of a previous study that investigated the negative impact of fear of COVID-19 on exacerbation of chronic pain in patients with fibromyalgia.¹⁷

As the present findings are being reported for the first time, and considering the lack of epidemiological studies to support our data, we present the results of some biological studies here, in terms of brain activity, particularly the functioning of the amygdala, which plays a central role in the expression of negative emotions, such as fear and anxiety.^31,32 Sugimoto et al.³³ explained the mechanism by which the mind and brain work to produce pain that spreads throughout the body; in animal models, an artificial chemogenetic excitation in the right central amygdala induced bilateral hind paw sensitization in rats without inflammation, which is one of the mechanisms of nociplastic pain. Thus, for workers experiencing either primary or secondary chronic pain, the fear of COVID-19 may have a significant impact on exacerbating chronic pain.

The presence of psychiatric diseases was also associated with the worsening of chronic pain. This finding is in accordance with the results of several previous studies: Birgenheir et al.³⁴ found that specific psychiatric diagnoses, including schizophrenia, bipolar disorder, and depression among veterans were associated with chronic pain, and Zis et al.³⁵ showed depression and chronic pain to be prevalent in the elderly. Our results showed that while chronic pain may be more common in the elderly, its worsening was observed more at a younger age. The participants who had planned hospital visits for their chronic pain diagnosis also presented more exacerbation of chronic pain during the state of emergency. It is possible that pain symptoms may have worsened because individuals had difficulty accessing routine medical care during the state of emergency, or because people voluntarily refrained from seeking medical care due to fear of infection. Of the 543 participants who reported that they had planned on going to the hospital to access medical care during the state of emergency, 130 (23.9%) reported that they could not see a doctor for a scheduled visit (data not shown).

In addition, we found that the more serious the fear of COVID-19, the more likely it was that labor productivity would be lost. This suggests that workers' fear of COVID-19 during the pandemic may have contributed to work performance loss directly as well as indirectly (through worsened pain). The questionnaire utilized in our study included questions regarding the prevalence of many types of comorbidities. Presenteeism for certain diseases, such as diabetes, hypertension, asthma, and cancer, has been found to reduce productivity.^8,36,37 The analysis results, after adjusting for the presence of comorbidities, suggested that fear of COVID-19 was an independent factor associated with decreased work productivity.

The present study has several limitations. First, this was a cross-sectional study and our results do not imply causation. In addition, various chronological question items were self-reported simultaneously, which may have resulted in recall bias. In addition, a time lag of several months occurred between the period when participants had become aware of the exacerbation of chronic pain and the period when they answered questions about the fear of COVID-19. Therefore, our result regarding the relationship between the fear of COVID-19 and the exacerbation of chronic pain may be potentially underestimated or overestimated. Further longitudinal studies designed to overcome this limitation are essential. Second, as the data used for this analysis were based on responses to an Internet-based survey, there is the potential for selection bias depending on individual habits of Internet usage. Third, this study was conducted during the early stages of the pandemic. It is generally expected that a virus will enter the endemic stage after a medium-term period. According to a certain theory, this medium-term period is presumed to last the next 5 or 6 years.³⁸ The public's anxiety and fear in relation to COVID-19 may change depending on the rate of infection, mortality rates, and tiredeness toward infection prevention measures. Thus, the timing of the study may affect the results. Furthermore, we could not determine whether individual participants had been diagnosed with COVID-19 or not. An actual COVID-19 infection could be a potential cofounder in the present study, as experience of infection may be related to level of fear. Instead, we considered epidemic level on residence in our analysis. Finally, the study had a relatively low response rate of 12.5%, raising concerns that respondents who participated in the study were more likely to worry about COVID-19 and experience symptoms such as anxiety than those who did not participate. Given the circumstances, the sample population in our study may not be truly representative of the general population. Despite these limitations, we did draw on a large sample of nationwide data and our study revealed an occupational health and productivity impairment problem that emerged during the COVID-19 pandemic.

In conclusion, severe fear of COVID-19 was positively associated with exacerbation of workers’ chronic pain during the state of emergency. In addition, the more severe the fear, the more likely it was that labor productivity would decrease. We submit that it is important to provide workers with appropriate education and information to help reduce their fear of COVID-19 and to assist them to access medical care when needed.