Deterioration of the Swallowing Function among Patients with COVID-19: A Propensity Score-matched Cohort Study

Abstract

Objective

This study aimed to investigate whether the swallowing function deteriorates more significantly following coronavirus disease 2019 (COVID-19) infection in comparison to other viral respiratory infections in patients with mild to moderate (grade 2) COVID-19.

Methods

We conducted a propensity score-matched cohort study at St. Luke's International Hospital in Tokyo, Japan, from January 2010 to March 2024. Elderly patients (≥70 years) admitted for viral respiratory infections, including influenza and COVID-19, were included. Patients with suspected bacterial infections, patients who were incapable of oral intake at admission (including those with enteral nutrition and gastrostomy), and patients who died during hospitalization were excluded. The primary outcome was deterioration in the swallowing function, defined as downgrade in food texture category from admission to discharge.

Results

During the study period, 505 COVID-19 patients and 242 patients with other viral infections were admitted. The mean age was 81.7 years (±7.6) and 401 patients (53.7%) were male. Patients with COVID-19 showed a significantly higher rate of swallowing deterioration in comparison to patients with other viral infections (44.7% vs. 36.6%, p=0.04). Specifically, among patients who consumed a full diet at admission, those with COVID-19 had a higher rate of swallowing deterioration than those with other viral infections (41.9% vs. 31.7%, p＜0.01).

Conclusion

COVID-19 was associated with a significant higher rate of downgrade in the food texture category in comparison to other viral respiratory infections, suggesting a potential impairment in the swallowing function. Given that this deterioration may contribute to prolonged hospitalization in COVID-19 patients, early intervention aimed at restoring and supporting swallowing function is warranted.

Introduction

Aspiration pneumonia is the sixth leading cause of death in Japan and is a serious issue in aging societies (1). Dysphagia, one of the causes of aspiration pneumonia, is a swallowing dysfunction that is commonly associated with cerebrovascular diseases, such as cerebral infarction, cerebral hemorrhage, and neurodegenerative diseases, such as Parkinson's disease (2).

Respiratory viral infections that cause common upper respiratory symptoms typically resolve naturally and rarely have lasting effects. Since the emergence of severe acute respiratory syndrome coronavirus 2 in 2020, the high mortality rate and long-term complications, such as long coronavirus disease 2019 (COVID-19) among the elderly, have become critical issues. According to data from the Centers for Disease Control and Prevention in 2020, the mortality rate from COVID-19 was significantly higher among individuals of ≥85 years of age, at 1,645.0 deaths per 100,000 population. This was 2.8 times greater than the rate for individuals of 75 to 84 years of age, which was 589.8 deaths per 100,000 population, and seven times higher than the rate for individuals of 65 to 74 years of age, which was 234.3 per 100,000. Among individuals of ≥85 years of age, 38.9% of COVID-19-related deaths occurred in nursing homes or long-term care facilities, in contrast the rates among individuals of 75-84 and 65-74 years of age were 19.2% and 9.7%, respectively. Aspiration pneumonia is the most frequent cause of death in older patients with SARS-CoV-2 Omicron-related pneumonia in Japan (3). In addition to its high mortality rate, COVID-19 has been associated with long-term complications including cognitive impairment (4-6) and persistent muscle weakness. These complications can exacerbate pre-existing swallowing dysfunction or contribute to new-onset dysphagia in affected individuals. Guidelines for physiotherapy interventions created by Australian physiotherapists and other experts recommend active screening for mobilization, exercise, and rehabilitation to counteract these effects (7).

Additionally, becoming bedridden due to the disuse syndrome weakens the cough reflex, further contributing to impairment of the swallowing function. This impairment in the physical function is a critical issue, particularly in elderly patients infected with COVID-19, who often experience impaired activities of daily living, leading to prolonged hospital stays and difficulties in securing transfer destinations.

Research on the impact of COVID-19 on the swallowing function has primarily focused on severe cases. Studies include six cases of tracheostomized patients weaned from mechanical ventilation (8), a video laryngoscopy study comparing 160 intensive care unit (ICU)-admitted COVID-19 patients with aspiration pneumonia (9), and a report on 235 ICU-admitted COVID-19 patients (10).

However, in severe cases, factors such as steroid use, prone positioning therapy, and intubation contribute significantly to swallowing dysfunction, making it difficult to isolate the impact of COVID-19.

To address this gap, our study aimed to investigate whether the swallowing function following COVID-19 infection deteriorates in comparison to other viral respiratory infections in patients with mild to moderate (grade 2) COVID-19 who are not admitted to the ICU. Specifically, we examined whether the deterioration in the swallowing function is greater in patients with COVID-19 than in those with other viral respiratory infections.

Materials and Methods

1．Study design

We conducted a propensity score-matched cohort study at St. Luke's International Hospital in Tokyo, Japan, from January 2010 to March 2024. We included all elderly patients (≥70 years) who were admitted due to viral respiratory infections, including influenza and COVID-19. The diagnosis of viral respiratory infection was made by each physician based on the results of rapid antigen tests, polymerase chain reaction (PCR) tests, and imaging (chest X-ray and computed tomography). We excluded patients suspected of having bacterial infections, patients who were unable to take oral medication at admission (including those with enteral nutrition and gastrostomy), and patients who died in the hospital. Our primary outcome was deterioration of the swallowing function at discharge. The ethical committee of St. Luke's International Hospital approved this study (approval number: 24-R039).

2．Deterioration of the swallowing function

For patients admitted to the hospital, information on activities of daily living, including food texture (full, soft, minced, pureed diet, or enteral nutrition), was obtained from histories taken from the patient or family members at the time of admission. Nurses assessed patients' dietary forms at home, and hospitalized patients received meals in the same form as they did at home. If a patient was at risk of aspiration due to impaired consciousness or swallowing dysfunction caused by COVID-19, a speech-language pathologist was consulted, and the dietary form was adjusted. Even during the COVID-19 pandemic, the nutrition department staff was able to provide food textures according to the patient's swallowing status. We also collected information on food texture at the time of discharge. We defined deterioration of the swallowing function as a downgrade in food texture category at discharge in comparison to that at admission.

3．Data collection

We obtained information about the diagnosis of viral respiratory infections, patient demographics, vital signs, laboratory data on admission, and Elixhauser comorbidities. All data were extracted from electronic medical records.

4．Statistical analyses

First, we categorized the patients into two groups: COVID-19 and other viruses (e.g., influenza and respiratory syncytial virus). We then compared the baseline characteristics between the groups. The propensity model was pre-specified and clinically important covariates were included in the model. We matched cases using a caliper width set to 0.2 times the standard deviation of the logit of the propensity score at a 1:1 ratio (other viruses: COVID-19), allowing for replacement. After propensity score matching, we compared the standardized mean differences (SMDs) for baseline characteristics between the pre- and post-matching groups. Subsequently, we compared the outcomes by group using a univariate analysis.

In the sub-analysis, we examined the chronological trends of the proportion of patients with deterioration of their swallowing function in relation to the emergence of different COVID-19 variants.

All analyses were performed in 2024 using Stata (ver. 16.0, StataCorp, USA).

Results

During the study period, 505 patients with COVID-19 and 242 patients with other viral infections, including 242 patients with influenza, were admitted to the hospital. The mean age (±standard deviation) of the cohort was 81.7 (±7.6) years, and 401 patients (53.7%) were male. Propensity scores were estimated in a logistic regression analysis, in which 14 clinically important covariates were pre-specified and entered by forced entry: age, heart rate, body temperature, systolic and diastolic blood pressure, hemoglobin, platelet count, serum albumin, aspartate aminotransferase (AST), γ-glutamyl transpeptidase (γ-GTP), prior history of neurological disorders, uncomplicated hypertension, psychosis, and systemic corticosteroid use at admission, with an area under the curve (AUC) of 0.81. An AUC value of ＞0.6 to ＜0.9 indicates an acceptable level of model performance.

After propensity score matching, 284 COVID-19 patients and 284 patients with other viral infections, including 284 with influenza, were identified. Table 1 compares the baseline characteristics and standardized differences between COVID-19 patients and those with other viral infections before and after propensity score matching.

Table 1.

Baseline Characteristics of the COVID-19 and Other Viral Infection Groups before and after Propensity Score Matching.

	Before propensity score matching							After propensity score matching
	Patients with COVID-19 (n=505)		Patients with Other virus (n=242)		p value	Standardized difference		Patients with COVID-19 (n=284)		Patients with Other virus (n=284)		p value	Standardized difference
Patient demographics
Age, mean (SD)	81.3	(7.6)	82.5	(7.6)	0.04	0.16		80.5	(6.8)	81.0	(7.7)	0.40	0.07
Male, n (%)	282	(55.8)	119	(49.2)	0.09	0.13		153	(53.9)	133	(46.8)	0.09	0.14
Length of stay, days (SD)	14.9	(15.3)	11.6	(19.2)	0.01	0.19		15.8	(17.6)	11.6	(14.2)	0.002	0.26
No. of transfer to nursing hospital, n (%)	112	(22.2)	29	(12.0)	0.001	0.27		69	(24.3)	22	(7.8)	<0.01	0.46
Dietary texture on admission, n (%)
Full diet	460	91.1	206	85.1	0.014	0.19		260	91.5	229	80.6	<0.01	0.30
Soft diet	24	4.8	29	12.0	<0.01	0.28		10	3.5	34	12.0	<0.01	0.32
Minced diet	9	1.8	4	1.7	0.899	0.01		6	2.1	4	1.4	0.52	0.05
Pureed diet	12	2.4	3	1.2	0.3	0.08		8	2.8	21	7.4	0.013	0.20
Vital signs on admission
Oxygen saturation (SpO2), %, (SD)	92.3	(4.8)	92.1	(4.5)	0.63	0.04		91.7	(5.2)	90.7	(11.6)	0.15	0.12
Systolic blood pressure, mmHg, (SD)	136.0	(24.9)	139.9	(25.6)	0.05	0.16		137.2	(25.9)	139.8	(24.6)	0.22	0.10
Diastolic blood pressure, mmHg, (SD)	81.3	(16.6)	76.6	(18.0)	<0.01	0.27		82.9	(17.0)	75.3	(16.9)	<0.01	0.45
Heart rate, beat per minute (SD)	87.6	(18.7)	94.7	(21.0)	<0.01	0.35		90.1	(20.0)	91.0	(23.5)	0.61	0.04
Respiratory rate, per minute (SD)	20.2	(5.2)	21.9	(6.1)	<0.01	0.29		21.1	(5.7)	20.7	(5.9)	0.43	0.07
Body temperature, ˚C (SD)	37.3	(1.0)	37.9	(1.1)	<0.01	0.60		37.4	(1.0)	37.6	(1.0)	<0.01	0.28
Laboratory test
Total protein, g/dL (SD)	6.9	(0.7)	7.0	(0.79)	0.075	0.14		6.9	(0.7)	5.7	(2.8)	<0.01	0.59
Serum albumin, g/dL (SD)	3.4	(0.5)	3.6	(0.5)	<0.01	0.36		3.4	(0.5)	3.6	(0.6)	<0.01	0.31
Blood urea nitrogen (BUN), mg/dL (SD)	25.0	(18.7)	23.2	(15.2)	0.182	0.11		24.7	(19.6)	22.2	(14.7)	0.08	0.15
Creatinine, mg/dL (SD)	1.3	(1.4)	1.2	(1.3)	0.12	0.12		1.2	(1.0)	1.1	(1.0)	0.19	0.11
Total bilirubin, mg/dL (SD)	0.6	(0.4)	0.7	(0.5)	0.01	0.19		0.6	(0.3)	0.6	(0.3)	0.69	0.03
Aspartate aminotransferase (AST), IU/L (SD)	37.4	(34.0)	67.0	(305.2)	0.032	0.14		39.1	(33.0)	68.8	(82.1)	<0.01	0.47
Alanine transaminase (ALT), IU/L (SD)	26.5	(28.6)	31.7	(56.7)	0.1	0.11		27.7	(27.2)	42.9	(80.3)	<0.01	0.25
Gamma-glutamyl transpeptidase (γ-GTP), IU/L (SD)	39.4	(44.7)	43.4	(52.6)	0.29	0.08		38.9	(40.2)	49.3	(66.8)	0.025	0.19
C reactive protein (CRP), mg/dL (SD)	5.7	(6.6)	6.2	(6.5)	0.28	0.08		6.5	(7.3)	6.8	(6.9)	0.64	0.04
White blood cell (WBC), 103/μL (SD)	7	(5)	8	(4)	0.04	0.17		8	(6)	7	(4)	0.30	0.09
Hemoglobin, g/dL (SD)	12.5	(2.1)	12.3	(1.9)	0.14	0.12		12.8	(2.0)	12.3	(2.3)	<0.01	0.24
Platelet, 103/μL (SD)	184.5	(70.9)	174.0	(62.1)	0.05	0.16		193.9	(77.4)	167.7	(54.9)	<0.01	0.39
Elixhauser Comorbidities, n (%)
Congestive heart failure	105	(20.8)	3	(1.2)	<0.01	0.66		11	(3.9)	36	(12.7)	<0.01	0.32
Cardiac arrhythmias	79	(15.6)	3	(1.2)	<0.01	0.46		13	(4.6)	36	(12.7)	<0.01	0.29
Valvular disease	34	(6.7)	0	(0.0)	<0.01	0.32		0	(0.0)	0	(0.0)	1.00	0.00
Pulmonary circulation Disorders	10	(2.0)	0	(0.0)	0.03	0.17		0	(0.0)	0	(0.0)	1.00	0.00
Peripheral vascular disorders	57	(11.3)	1	(0.4)	<0.01	0.41		3	(1.1)	1	(0.4)	0.32	0.08
Hypertension, uncomplicated	161	(31.9)	2	(0.8)	<0.01	0.75		13	(4.6)	8	(2.8)	0.27	0.09
Hypertension, complicated	2	(0.4)	0	(0.0)	0.33	0.08		0	(0.0)	0	(0.0)	1.00	0.00
Paralysis	4	(0.8)	0	(0.0)	0.17	0.11		0	(0.0)	0	(0.0)	1.00	0.00
Other neurological disorders	28	(5.5)	2	(0.8)	<0.01	0.24		6	(2.1)	8	(2.8)	0.59	0.05
Chronic pulmonary disease	97	(19.2)	2	(0.8)	<0.01	0.54		12	(4.2)	35	(12.3)	<0.01	0.29
Diabetes, uncomplicated	7	(1.4)	0	(0.0)	0.07	0.14		0	(0.0)	0	(0.0)	1.00	0.00
Diabetes, complicated	19	(3.8)	0	(0.0)	<0.01	0.24		0	(0.0)	0	(0.0)	1.00	0.00
Hypothyroidism	18	(3.6)	1	(0.4)	0.01	0.20		5	(1.8)	7	(2.5)	0.56	0.05
Renal failure	51	(10.1)	0	(0.0)	<0.01	0.40		0	(0.0)	0	(0.0)	1.00	0.00
Liver disease	44	(8.7)	0	(0.0)	<0.01	0.37		0	(0.0)	0	(0.0)	1.00	0.00
Peptic ulcer disease excluding bleeding	112	(22.2)	3	(1.2)	<0.01	0.69		14	(4.9)	36	(12.7)	0.001	0.28
AIDS/HIV	1	(0.2)	0	(0.0)	0.49	0.05		0	(0.0)	0	(0.0)	1.00	0.00
Lymphoma	15	(3.0)	0	(0.0)	<0.01	0.21		0	(0.0)	0	(0.0)	1.00	0.00
Metastatic cancer	11	(2.2)	0	(0.0)	0.02	0.18		0	(0.0)	0	(0.0)	1.00	0.00
Solid tumor without metastasis	69	(13.7)	1	(0.4)	<0.01	0.45		6	(2.1)	28	(9.9)	<0.01	0.33
Rheumatoid arthritis/collagen vascular diseases	28	(5.5)	0	(0.0)	<0.01	0.29		0	(0.0)	0	(0.0)		0.00
Coagulopathy	24	(4.8)	0	(0.0)	<0.01	0.27		0	(0.0)	0	(0.0)	1.00	0.00
Obesity	1	(0.2)	0	(0.0)	0.49	0.05		0	(0.0)	0	(0.0)	1.00	0.00
Weight loss	6	(1.2)	0	(0.0)	0.09	0.13		0	(0.0)	0	(0.0)	1.00	0.00
Fluid and electrolyte disorders	80	(15.8)	1	(0.4)	<0.01	0.50		5	(1.8)	7	(2.5)	0.56	0.05
Blood loss anemia	2	(0.4)	0	(0.0)	0.33	0.08		0	(0.0)	0	(0.0)	1.00	0.00
Deficiency anemia	63	(12.5)	2	(0.8)	<0.01	0.41		4	(1.4)	8	(2.8)	0.24	0.10
Alcohol abuse	2	(0.4)	0	(0.0)	0.33	0.08		0	(0.0)	0	(0.0)	1.00	0.00
Drug abuse	0	(0.0)	0	(0.0)	1.00	0.00		0	(0.0)	0	(0.0)	1.00	0.00
Psychoses	9	(1.8)	1	(0.4)	0.13	0.12		2	(0.7)	1	(0.4)	0.56	0.05
Depression	42	(8.3)	1	(0.4)	<0.01	0.34		4	(1.4)	8	(2.8)	0.24	0.10

Even after propensity score matching, several baseline characteristics remained imbalanced (absolute SMD ＞0.10), including sex, length of stay, transfer to a nursing hospital, selected dietary texture at admission categories (soft, pureed), vital signs (diastolic blood pressure, oxygen saturation, body temperature), laboratory values (total protein, serum albumin, blood urea nitrogen, creatinine, AST, ALT, γ-GTP, hemoglobin, and platelets), and comorbidities such as congestive heart failure, cardiac arrhythmias, chronic pulmonary disease, peptic ulcer disease, and solid tumor without metastasis, as summarized in Table 1. However, no clinically significant differences were observed in the vital signs or laboratory test results. COVID-19 patients had a longer hospital stay and a higher rate of transfer to nursing homes despite being more likely to consume a full diet at admission, regardless of matching. Regarding deterioration of the swallowing function, COVID-19 patients were more likely to experience a downgrade in dietary texture from admission to discharge than patients with other viral infections (44.7% vs. 36.6%, p=0.04) (Table 2, Fig. 1). Specifically, among the patients who consumed a full diet at admission, those with COVID-19 had a significantly higher rate of swallowing deterioration than those with other viral infections (41.9% vs. 31.7%, p＜0.01). Fig. 2 illustrates the chronological trends in the proportion of patients with swallowing deterioration across the different COVID-19 variant waves. The overall proportion of patients experiencing swallowing deterioration was approximately 40% over time. The 100% value in late 2021 was because only one COVID-19 patient was admitted during that period.

Table 2.

Dietary Texture Downgrade at Discharge from Admission.

	COVID-19 (n=284)		Other virus (n=284)		p value
Dietary texture downgraded at discharge from admission, n (%)	203	(44.7)	83	(36.6)	0.04
Downgraded at discharge from full diet at admission	191	(41.9)	72	(31.7)	<0.01
Downgraded at discharge from soft diet at admission	5	(1.06)	0	(0.00)	0.112
Downgraded at discharge from minced diet at admission	5	(1.06)	3	(1.41)	0.804
Downgraded at discharge from pureed diet at admission	3	(0.70)	8	(3.52)	<0.01

Figure 1.

Dietary texture downgrade at discharge.

Figure 2.

Annual proportion of swallowing function deterioration and number of COVID-19 patients.

Discussion

In our study, COVID-19 patients had a longer hospital stay and a higher rate of transfer to nursing homes despite being more likely to consume a full diet at the time of admission. With regard to deterioration of the swallowing function, COVID-19 patients were more likely to experience a downgrade in dietary texture from admission to discharge than those with other viral infections. Specifically, among patients who were on a full diet at admission, those with COVID-19 showed a significantly higher rate of swallowing deterioration than patients with other viral infections. Furthermore, when we analyzed the data from 2020 to 2024, the overall proportion of patients experiencing swallowing deterioration consistently remained at approximately 40%.

A study investigating the laryngopharyngeal manifestations of the Delta and Omicron variants of COVID-19 found that the Delta variant was more likely to cause neurological involvement of the vocal folds, manifesting as paresis and paralysis (11). This study highlighted that laryngeal paralysis and motor dysfunction are common complications of COVID-19, potentially resulting from virus-induced innervation damage. Although the exact mechanisms of nerve damage remain unclear, it is hypothesized that the virus may directly induce neurotoxicity or trigger autoimmune vasculitis of the nerves. Furthermore, post-viral vagal neuropathy, which is associated with COVID-19, may lead to sensory and motor dysfunction of the vagus nerve.

Our study had several limitations. First, it was a retrospective study. Until May 2023, even mild cases of COVID-19 were subject to mandatory hospitalization by government regulations, resulting in many patients being admitted under administrative orders. Therefore, unlike other viral infections, there may have been a selection bias. However, this study focused on elderly patients, many of whom were likely hospitalized because of the severity of their condition. Moving forward, we aim to collect and analyze additional data from patients after May 2023. In addition, data extraction for other viral infections was limited. In Japan, the Film-Array Respiratory Panel (bioMérieux, Marcy-l'Étoile, France), a multiplex PCR method for detecting the causative viruses of respiratory infections, received national health insurance coverage in November 2019. Its use has become more widespread in clinical settings since the onset of the SARS-CoV-2 pandemic in 2020. Before this, antigen testing for viruses such as influenza, respiratory syncytial virus, and human metapneumovirus was primarily used, especially in pediatric patients, leading to lower diagnostic accuracy for respiratory viral infections. As a result, many cases may have gone undetected, potentially underestimating the number of patients in the other viral infection group. However, this study included hospitalized patients with viral respiratory infections, and many influenza patients could be accurately diagnosed and confirmed positive, suggesting that the impact of this bias is likely to be minimal. Moving forward, the increased use of multiplex PCR testing is expected to facilitate more comprehensive accumulation of data on respiratory viral infections. Furthermore, the assessment of dietary texture may not solely reflect disuse syndrome; it can also be influenced by factors such as tooth loss or denture use. Therefore, it does not precisely capture the true swallowing function. In the future, we aim to explore more quantitative methods to accurately assess the swallowing function. Although food textures were promptly adjusted during the COVID-19 pandemic, there were instances in the very early stages in which adjustments were not made. However, the effects in such cases were relatively small. Regarding the appropriateness of the initial diet form at admission, if the patient's condition deteriorated, ward nurses made physician-ordered dietary changes. However, there may be instances where these adjustments occurred after scheduled meal changes, resulting in the modification being reflected in the subsequent meal order. Ideally, the first three meal deliveries should have been considered a washout period, and the diet texture should have been assessed starting from the fourth meal. Crucially, it is possible that the dietary texture was intentionally lowered upon admission, considering the severity of the patient's condition (e.g., pneumonia status or consciousness level) or as a proactive safety measure. If such preemptive downgrades occurred, particularly if more frequently applied to COVID-19 patients owing to perceived higher acuity, the true impact of COVID-19 on the swallowing function might be underestimated in our study, as the baseline from which deterioration is measured would already be lowered. In this retrospective analysis using electronic medical records, we were unable to extract sufficient information on smoking history, vaccination status, and baseline activities of daily living owing to system limitations. Smoking is a known risk factor for swallowing reflex impairment, potentially through attenuation of the pharyngoglottal closure reflex, which plays a critical role in aspiration prevention (12). This finding may be relevant to the interpretation of post-COVID-19 dysphagia.

Nevertheless, in the case of COVID-19, many admissions were scheduled under the Japanese system, suggesting that the impact would be similar across both groups for the majority of cases, allowing for a comparative analysis of differential effects.

The severity of COVID-19 varies depending on the circulating variant, and although our study tracked temporal changes in the swallowing function, the sample size was insufficient to draw definitive conclusions. Although the mechanism underlying the differences in swallowing dysfunction between virus variants has not been fully clarified, various studies have indicated that the Delta variant is associated with a higher risk of hospitalization, ICU admission, oxygen therapy, ventilation, and death in comparison to the Omicron variant (13,14). This may suggest a potential link to deterioration of the swallowing function. Furthermore, while our study demonstrates a significant association between COVID-19 and deterioration of the swallowing function that may contribute to prolonged hospitalization, we acknowledge that the current findings do not fully elucidate the comprehensive mechanisms or causality behind extended lengths of stay. Further studies are warranted to fully explain the interplay between swallowing deterioration and prolonged hospitalization.

Additionally, this study was limited to COVID-19 patients who were hospitalized at a single facility. As the swallowing function may improve over the long term, further investigation after transfer to other facilities is warranted. In this study, impairment of the swallowing function was defined as a downgrade in dietary texture from admission to discharge. Ideally, an objective assessment of the swallowing function should be conducted using methods such as the Repetitive Saliva Swallowing Test and cervical auscultation or through examinations performed by otolaryngologists, such as swallowing video fluorography and swallowing video endoscopy. However, owing to infection control measures during the COVID-19 pandemic, these assessments were restricted and could not be performed. Additionally, changes in dietary texture are influenced by multiple factors beyond the swallowing function, including taste perception and individual preferences, making precise evaluation challenging. Prospective objective evaluation methods are needed for a more accurate assessment of the swallowing function. In our study, a significant decrease in dietary texture was observed in COVID-19 patients in comparison to patients with other viral infections, such as influenza. This finding suggests that COVID-19 may contribute to swallowing dysfunction. While this deterioration may contribute to prolonged hospitalization in COVID-19 patients, we acknowledge that the full mechanisms or causality behind extended lengths of stay require further elucidation in future research. Nevertheless, given the potential for dietary texture downgrades to prolong hospitalization, early intervention aimed at restoring and supporting the swallowing function is considered necessary. Future research should also investigate the swallowing function using objective measures.

Consent for case report: Patient consent has been obtained.

The authors state that they have no Conflict of Interest (COI).