PHWR Public Health Weekly Report

As the Republic of Korea (ROK) transitions into a super-aged society, the demand for long-term care facilities is increasing rapidly [1]. Residents of these facilities are predominantly elderly and are particularly vulnerable to respiratory infectious diseases, such as influenza and coronavirus disease 2019 (COVID-19), owing to underlying medical conditions and age-related immune decline [2,3]. The shared use of communal spaces, including bedrooms, activity rooms, and dining areas, by large numbers of residents within enclosed indoor environments substantially increases the risk of cluster infections through airborne and droplet transmission [2,4,5].

The Ministry of Land, Infrastructure and Transport’s Rules on Facility Standards for Buildings [Attached Table 1-6] require nursing homes, classified under facilities for the elderly and young with a total floor area of ≥1,000 m², to install ventilation systems providing 36 m³/h of outdoor air per person [6]. The Ministry of Health and Welfare additionally recommends a minimum outdoor air ventilation rate of at least 2 air changes per hour (ACH) and a total ventilation rate of at least 6 ACH, including recirculated air, for wards and intensive care units [7]. Furthermore, the National Health Insurance Service’s evaluation criteria for long-term care facilities mandate routine ventilation practices (at least three times per day, with a minimum of 10 minutes of natural ventilation per session) and maintenance of a ventilation checklist; however, they do not include assessment of actual ventilation rates expressed as volumetric flow (m³/h) or ACH [8]. The World Health Organization (WHO) guidelines on natural ventilation likewise emphasize the importance of ensuring adequate ventilation in healthcare facilities for infection prevention and control [9].

The recurrence of large outbreaks in long-term care facilities during the COVID-19 pandemic has underscored the critical importance of indoor air quality management and adequate ventilation. However, studies that directly measure natural and mechanical ventilation rates and quantitatively assess infection risk in Korean long-term care facilities remain limited. Accordingly, this study aimed to evaluate the ventilation status of nursing homes and group homes in Seosan City by measuring ventilation rates and to provide evidence to inform improved ventilation standards for infection-vulnerable facilities through estimation of airborne transmission risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using Korean-virus emission & airborne transmission assessment program (K-VENT 3.1) [10].

1. Study Sites

This study was conducted between April 23 and May 21, 2025, and targeted long-term care facilities in Seosan City, Chungcheongnam-do Province, ROK. A total of 27 facilities were included, comprising 23 nursing homes and 4 group homes, all of which are classified as medical welfare facilities for the elderly under the Welfare of Senior Citizens Act. On-site surveys were performed with the cooperation of the Seosan Health Center and with informed consent obtained from facility directors.

At each facility, one bedroom routinely occupied by residents was selected for assessment; if an energy recovery ventilator (ERV) was installed, that bedroom was additionally evaluated. General facility characteristics were systematically collected, including building age (categorized as new, general, or old), the presence and type of mechanical ventilation systems, and bedroom ventilation mode (natural, mechanical, or combined).

2. Definition of Ventilation Methods

The ventilation rate within the target space is determined by air infiltration through building envelope leakage, natural ventilation, and mechanical ventilation. Infiltration and natural ventilation rates vary according to building age, floor plan and window type, window area, indoor–outdoor temperature differences, and outdoor wind speed [10].

For the purpose of estimating infiltration, building age was categorized as new (<3 years since construction), general (≥3 to <10 years), or old (≥10 years). Natural ventilation refers to the unforced inflow and outflow of air through windows, gaps, and vents driven by wind, indoor–outdoor temperature differences, and pressure gradients. Mechanical ventilation refers to systems that maintain controlled airflow and air exchange rates using components such as fans, ducts, and ERVs. Bedroom ventilation methods were classified as “natural ventilation” when only natural ventilation was used, “mechanical ventilation” when only mechanical ventilation was used, and “combined ventilation” when both methods operated concurrently.

3. Measurement of Ventilation Rate (m³/h) and Calculation of ACH

Ventilation rates were measured using a laser rangefinder (MAGPIE SABER X), a hot-wire anemometer (Testo 405-V1, Testo), and a vane anemometer with a square funnel (Testo 417 and testo 4170, Testo). The volume (m³) of each bedroom was calculated by measuring room length, width, and height with the laser rangefinder.

For natural ventilation assessment, the horizontal and vertical dimensions of windows in each bedroom were measured using the laser rangefinder. When multiple windows were located on the same wall, their lengths were summed.

Window types were classified into four categories according to K-VENT 3.1: fixed, awning, casement, and sliding. Bedroom floor plan types were categorized into six types defined in K-VENT 3.1: one-sided open, composite open, double-sided open, single-loaded corridor, double-loaded corridor (one-sided open), and double-loaded corridor (double-sided open). All operable windows were fully opened, and the average outdoor wind speed (m/s) was measured using the hot-wire anemometer.

For mechanical ventilation, the hourly airflow rate was measured at all supply and exhaust vents within each bedroom using a vane anemometer with a square funnel. When an ERV was installed, the average air velocity (m/s) was measured using a hot-wire anemometer, and the hourly ventilation rate was calculated using the following equation:

Ventilation rate (m³/h)=air velocity (m/s)×supply or exhaust area (m²)×3,600 (s/h).

ACH for both natural and mechanical ventilation were calculated using K-VENT 3.1.

4. Ventilation Standards and Evaluation Criteria

According to regulations of the Ministry of Land, Infrastructure and Transport, nursing homes with a total floor area of ≥1,000 m² are required to provide a ventilation rate of 36 m³/h per person. The guideline-recommended minimum outdoor air intake rate of at least 2 ACH, specified for hospital wards and intensive care units, was adopted as the reference standard for evaluating bedroom ventilation. In addition, the ventilation management guidelines prescribed in the National Health Insurance Service’s Detailed Enforcement Rules for the Evaluation and Management of Long-Term Care Facilities—which require natural ventilation at least three times per day for a minimum of 10 minutes per session—were applied to assess routine ventilation practices in the surveyed facilities.

5. Infection Risk Assessment (K-VENT 3.1)

The risk of airborne transmission of respiratory infectious diseases was estimated using K-VENT 3.1, developed by the Korea Disease Control and Prevention Agency. Model parameters were defined as follows: the SARS-CoV-2 Delta variant was selected as the target virus; one infected individual was assumed; the activity level was set to resting (oral breathing); and the exposure duration was 3 hours. The number of exposed individuals was determined by subtracting the single infected individual from the maximum occupancy of each bedroom, resulting in facility-specific exposure scenarios (e.g., three exposed individuals in a four-person room, two in a three-person room, and one in a two-person room).

External environmental parameters included outdoor wind speed and ambient temperature. Five-year (2020–2024) May averages for Seosan City—2.26 m/s for wind speed and 17.1°C for temperature—were applied. The estimated infection risk (%) was calculated for each scenario and compared between natural ventilation and combined ventilation conditions.

6. Statistical Analysis

The 23 nursing homes were labeled A through W, and the four group homes were labeled AA, BB, CC, and DD. Normality of the differences in estimated infection risk between natural ventilation and combined ventilation conditions was assessed using the Shapiro–Wilk test. When the normality assumption was satisfied, a paired t-test was performed to estimate the mean difference and its 95% confidence interval (CI) between the two ventilation conditions. Effect size was quantified using Cohen’s d to evaluate the magnitude of the difference between natural and combined ventilation. Cohen’s d-values were interpreted as small (≤0.2), medium (0.5), and large (≥0.8). All statistical analyses were conducted using R version 4.2.2, with statistical significance defined as p<0.05.

1. General Characteristics of the Study Sites

Among the 27 study sites, 20 facilities (74.0%) were classified as general buildings with 3–10 years of use, five (18.6%) as old buildings with more than 10 years of use, and two (7.4%) as new buildings with less than 3 years of use. The frequency of natural ventilation was ≥6 times per day in 11 facilities (40.8%), ≥3 to <6 times per day in 10 facilities (37.0%), and <3 times per day in six facilities (22.2%). Overall, 21 of the 27 facilities (77.8%) met the long-term care facility evaluation requirement of natural ventilation at least three times per day. The duration of natural ventilation per session was ≥10 to <30 minutes in 23 facilities (85.2%) and ≥30 minutes in three facilities (11.1%), with 26 facilities (96.3%) meeting the minimum criterion of 10 minutes per session (Table 1).

Table 1 General characteristics of the facilities

Characteristic		Nursing home (n=23)	Group home (n=4)	Total (n=27)
Building type (yr)	<3 (new)	2 (8.7)	0 (0.0)	2 (7.4)
	3–10 (standard)	17 (73.9)	3 (75.0)	20 (74.0)
	≥10 (old)	4 (17.4)	1 (25.0)	5 (18.6)
Mean hourly combined ventilation rate’ room (ACH)		1.6±1.0	0.8±0.6	1.4±0.9
Hourly combined ventilation rate’ room (ACH)	<2	18 (78.3)	4 (100.0)	22 (81.5)
	2–6	5 (21.7)	0 (0.0)	5 (18.5)
	≥6	0 (0.0)	0 (0.0)	0 (0.0)
Ventilation method in residents’ room	Natural only	5 (21.7)	3 (75.0)	8 (29.6)
	Mechanical only	1 (4.3)	0 (0.0)	1 (3.7)
	Combineda)	17 (73.9)	1 (25.0)	18 (66.7)
Mean number of natural ventilation events per day (times)		5.7±2.6	5.3±1.1	5.5±2.3
Daily frequency of natural ventilation (times)	<3	6 (26.1)	0 (0.0)	6 (22.2)
	3–6	7 (30.4)	3 (75.0)	10 (37.0)
	≥6	10 (43.5)	1 (25.0)	11 (40.8)
Mean duration of natural ventilation per event (min)		16.5±11.2	12.5±4.3	15.4±10.4
Duration of natural ventilation per event (min)	<10	1 (4.3)	0 (0.0)	1 (3.7)
	10–30	19 (82.6)	4 (100.0)	23 (85.2)
	≥30	3 (13.0)	0 (0.0)	3 (11.1)
Mean hourly natural ventilation rate (ACH)		1.0±1.0	0.8±0.7	0.9±1.0
Hourly natural ventilation rate (ACH)	<2	20 (87.0)	4 (100.0)	24 (88.9)
	2–6	3 (13.0)	0 (0.0)	3 (11.1)
	≥6	0 (0.0)	0 (0.0)	0 (0.0)
Mean hourly mechanical ventilation rate (ACH)		0.4±0.2	0.1±0	0.4±0.2
Hourly mechanical ventilation rate (ACH)	<2	18 (100.0)	1 (100.0)	19 (100.0)
	2–6	0 (0.0)	0 (0.0)	0 (0.0)
	≥6	0 (0.0)	0 (0.0)	0 (0.0)
Mechanical ventilation system	HVAC system	4 (17.4)	1 (25.0)	5 (18.6)
	Heat recovery ventilator	10 (43.5)	0 (0.0)	10 (37.0)
	HVAC+ERV	3 (13.0)	0 (0.0)	3 (11.1)
	Exhaust fan only	1 (4.3)	0 (0.0)	1 (3.7)
	Not installed	5 (21.7)	3 (75.0)	8 (29.6)

Unit: number (%) or mean±standard deviation. ACH=air changes per hour; HVAC=heating, ventilation, and air conditioning; ERV=energy recovery ventilator. ^a)Combined ventilation refers to the concurrent use of natural and mechanical ventilation..

Mechanical ventilation systems were installed in 19 facilities (70.4%), including 10 facilities (37.0%) equipped with ERVs, five (18.6%) with heating, ventilation, and air-conditioning(HVAC) systems, three (11.1%) with both HVAC systems and ERVs, and one (3.7%) with a simple exhaust fan. The remaining eight facilities (29.6%) had no mechanical ventilation systems. Combined ventilation was the most common ventilation mode, observed in 18 facilities (66.7%), followed by natural ventilation alone in eight facilities (29.6%) and mechanical ventilation alone in one facility (3.7%), where natural ventilation was not feasible (Table 1).

2. Natural and Mechanical Ventilation and ACH in Bedrooms by Facility

The mean daily frequency of natural ventilation was 5.7±2.6 times in nursing homes and 5.3±1.1 times in group homes. The mean duration per natural ventilation session was 16.5±11.2 minutes in nursing homes and 12.5±4.3 minutes in group homes (Table 1). The mean ACH during natural ventilation was 0.9±1.0 across 26 facilities, whereas the mean ACH during mechanical ventilation was 0.4±0.2 across 19 facilities equipped with mechanical ventilation systems. Overall, the mean bedroom ACH was 1.4±0.9 across all 27 facilities; nursing homes averaged 1.6±1.0 ACH, while group homes averaged 0.8±0.6 ACH (Table 1).

One of the 23 nursing homes had no natural ventilation because the windows were non-operable.

Only three facilities (11.1%) achieved an air change rate of at least 2 ACH through natural ventilation alone; in these facilities, windows were kept continuously open to maintain ventilation (Table 1). No facilities met the ≥2 ACH criterion through mechanical ventilation alone.

Overall, five nursing homes (18.5%) achieved at least 2 ACH in bedrooms, whereas none of the group homes met this threshold (Table 1).

3. ACH in Spaces with ERV Installation

Based on measured mechanical ventilation rates in 13 nursing homes equipped with ERVs (A, C, D, F, G, K, L, M, O, R, S, T, and W), the mean ACH under combined ventilation conditions was 1.5±1.1. In contrast, the mean ACH calculated using the certified ventilation capacity (cubic meters per hour) was 2.5±1.5 (Table 2).

Table 2 Ventilation rates and air changes per hour by facility

Bed room		Room volume (m3)	Measured ventilation						Certified ventilation
			Infiltration volume (m3/h)	Natural ventilation volume (m3/h)	Mechanical ventilation volume (m3/h)	Total ventilation volume (m3/h)	ACH based on measured total volume (ACH)		Certified volumea) (CMH)	ACH based on measured certified volume (ACH)
4	A	75.0	18.8	6.6	6.2	31.5	0.4		100	1.7
	B	67.0	23.4	9.2	6.5	39.1	0.6		Exhaust fan only	-
	C	77.2	19.3	0.0	38.9	58.2	0.8		100	1.6
	D	96.4	24.1	13.5	36.1	73.7	0.8		70	1.1
	G	64.4	16.1	12.2	33.7	62.0	1.0		100	2.0
	H	79.1	19.8	70.4	0.0	90.2	1.1		Not installed	-
	I	97.5	14.6	25.9	66.2	106.7	1.1		HVAC system	-
	K	85.2	21.3	60.4	15.9	97.6	1.1		80	1.9
	L	82.7	20.7	35.3	39.8	95.8	1.2		100	1.9
	M	62.2	15.6	28.0	40.0	83.6	1.3		70	1.8
	N	85.1	29.8	89.3	0.0	119.1	1.4		Not installed	-
	O	59.1	14.8	36.5	33.1	84.4	1.4		100	2.6
	P	69.2	24.2	75.5	0.0	99.7	1.4		Not installed	-
	Q	72.0	18.0	89.6	11.7	119.3	1.7		HVAC system	-
	R	75.4	18.9	74.6	40.0	133.3	1.8		70	2.2
	V	66.0	16.5	213.3	0.0	229.8	3.5		Not installed	-
	AA	66.4	16.6	8.1	0.0	24.7	0.4		Not installed	-
	CC	64.9	16.2	22.6	0.0	38.8	0.6		Not installed	-
	DD	71.3	17.8	106.8	5.9	130.5	1.8		HVAC system	-
3	E	65.7	9.9	19.9	24.6	54.3	0.8		HVAC system	-
	F	100.1	25.0	14.5	46.7	86.2	0.9		70	1.1
	J	57.7	14.4	31.1	19.0	64.5	1.1		HVAC system	-
	S	60.9	15.2	61.6	43.4	120.2	2.0		100	2.9
	U	59.9	15.0	129.3	0.0	144.3	2.4		Not installed	-
	W	39.9	10.0	164.2	18.3	192.5	4.8		100	6.9
	BB	58.6	14.7	8.6	0.0	24.3	0.4		Not installed	-
2	T	34.1	8.5	60.1	6.1	74.7	2.2		80	4.4

Total ventilation volume=infiltration volume+natural ventilation volume+mechanical ventilation volume; ACH based on measured total volume=total ventilation volume÷room volume; ACH based on certified volume=(infiltration volume+natural ventilation volume+certified volume)÷room volume; ACH=air changes per hour; CMH=cubic meter per hour (m³/h); HVAC=heating, ventilation, and air conditioning. ^a)Calculations based on the “medium” fan setting for each product; when information for the medium setting was unavailable, the “high” setting was used..

When ERVs were operated at a low or weak setting, only two facilities (S and T) achieved at least 2 ACH under combined ventilation. Under the assumption that ERVs were operated at a medium setting or higher, six facilities (G, O, R, S, T, and W) met the ≥2 ACH criterion during combined ventilation (Table 2).

4. Reduction in Infection Risk with Concurrent Mechanical Ventilation

Estimated infection risk was compared between natural ventilation alone and combined natural and mechanical ventilation in 19 facilities equipped with mechanical ventilation systems (18 nursing homes and one group home). In all facilities, the estimated infection risk decreased when mechanical ventilation was applied concurrently. The largest reduction was observed in nursing homes I, where the estimated infection risk decreased by 23.2%p, from 97.1% under natural ventilation alone to 73.9% with combined ventilation (Figure 1). The difference in estimated infection risk between natural ventilation alone and combined ventilation satisfied the normality assumption (Shapiro–Wilk test, p=0.101). A paired t-test demonstrated a statistically significant mean reduction of 11.4±6.9%p (p=0.001, 95% CI: 7.9–14.7), with a moderate effect size (Cohen’s d=0.57).

Figure 1. Estimated risk of respiratory infection in bedrooms by facility and mechanical ventilation status

When infection risk was recalculated for the 13 nursing homes equipped with ERVs (A, C, D, F, G, K, L, M, O, R, S, T, and W), assuming operation at the maximum ventilation capacity (high setting), the estimated infection risk decreased in all facilities compared with natural ventilation alone (Figure 1).

When the maximum ventilation capacity was applied, the largest reduction in estimated infection risk was observed in nursing homes A, where the risk decreased by 45.5%p, from 98.7% under natural ventilation alone to 53.2% with combined ventilation (Figure 1). The differences in estimated infection risk between natural ventilation alone and combined ventilation under the maximum ERV ventilation scenario satisfied the normality assumption (p=0.184). A paired t-test demonstrated a statistically significant mean reduction of 33.8±9.8%p, p=0.001 (95% CI: 28.0–32.6), with a large effect size (Cohen’s d=1.28), across the 13 nursing homes equipped with ERVs.

This study conducted a survey-based assessment of natural and mechanical ventilation rates in elderly medical welfare facilities in Seosan City and quantitatively evaluated the risk of airborne transmission of SARS-CoV-2 using the K-VENT 3.1 program. The findings indicate that behavior-based ventilation management guidelines, such as natural ventilation at least three times daily for a minimum of 10 minutes per session, as required in long-term care facility evaluations, were met in many facilities. However, despite adherence to these operational criteria, 24 of the 27 facilities (88.9%) exhibited an average bedroom air change rate below 2 ACH during natural ventilation. Although the average outdoor wind speed applied in the infection risk assessment exceeded the 1 m/s value suggested in the WHO guidelines for natural ventilation, reflecting the coastal geographical characteristics of the study area, adequate air exchange could not be reliably ensured through ventilation frequency and duration alone [9]. These findings highlight the substantial variability in factors influencing natural ventilation performance across facilities, including window size, degree of window opening, and outdoor wind speed and temperature.

The mean bedroom ACH was 1.4±0.9, underscoring the importance of mechanical ventilation as a key measure for reducing infection risk. Compared with natural ventilation alone, the addition of mechanical ventilation reduced the estimated infection risk by an average of 11.4±6.9%p, with a maximum reduction of 23.2%p observed in individual facilities.

When ERVs were assumed to operate at their maximum ventilation capacity, the estimated infection risk across the 13 nursing homes decreased by an average of 33.8±9.8%p relative to natural ventilation alone, with a maximum reduction of 45.5%p.

The magnitude of these reductions was supported by effect size analysis, with Cohen’s d-values of 0.57 for measured ventilation rates and 1.28 for maximum ventilation rates. These effect sizes indicate that the observed reductions in estimated infection risk were not only statistically significant but also of practical relevance.

Although ERVs are typically operated at a low setting during routine conditions, it is critical to strengthen infection control by increasing operation to medium or high settings during outbreaks of respiratory infectious diseases to minimize transmission risk.

In this survey, when ERVs were assumed to operate at a medium setting corresponding to the certified ventilation rate, only six of the 13 facilities equipped with ERVs achieved a bedroom ventilation rate of at least 2 ACH, whereas the remaining seven facilities did not meet this threshold. This finding likely reflects the practice of installing mechanical ventilation systems with uniform capacities in long-term care facilities without adequate consideration of room volume. These results highlight the need for procedures to verify whether required ACH levels can be achieved by reviewing outdoor air intake at the design stage, using assessment tools such as K-VENT, when installing ERVs.

This study has several limitations. First, K-VENT 3.1 is sensitive to assumed input parameters, including virus type, virus emission rates associated with the infected individual’s activity level, and the respiratory rate and exposure duration of susceptible individuals; consequently, estimated infection risks may differ from actual transmission outcomes. Second, real-time CO₂ concentrations were not measured concurrently. Unlike the 2024 study Measuring Ventilation and Contamination in Long-term Care Hospitals to Study Improvements, this limitation precluded direct correlation of ventilation rates with indoor air quality indicators [11]. Third, ventilation rates were not measured under medium or high ERV operating settings, preventing direct comparison between measured ventilation performance and certified ventilation capacity. Despite these limitations, the findings consistently indicate that natural ventilation alone was insufficient in many facilities and that concurrent operation of ERVs is necessary to achieve a stable and adequate air change rate.

The policy implications of this study are as follows. First, there is a need to gradually introduce air change rate (ACH) standards and mandatory mechanical ventilation requirements into the evaluation criteria for long-term care facilities, with grading systems differentiated by ventilation approach, such as natural ventilation, exhaust fan installation, and ERVs. Second, regular measurement and monitoring of ventilation performance should be institutionalized at the local government level, accompanied by financial support and incentive mechanisms for mechanical ventilation upgrades and equipment replacement. Third, training programs for facility managers should be strengthened to improve competency in determining appropriate ventilation capacities, selecting operational settings, and implementing proper maintenance of mechanical ventilation systems.

In addition, extending K-VENT-based infection risk estimation to other multi-use facilities, including schools, daycare centers, and welfare facilities for persons with disabilities, could support the development of standardized ventilation management guidelines for community-level infectious disease preparedness and response.

Ethics Statement: Not applicable.

Funding Source: None.

Acknowledgments: We express our sincere gratitude to the Health Policy Division of Chungcheongnam-do, the staff of Seosan Public Health Center, and the managers and caregivers of the participating long-term care facilities for their cooperation with on-site measurements and data collection. We also thank Senior Researcher Sang-Hwan Bae and Researcher Jung-Yeon Yoo of the Korea Institute of Civil Engineering and Building Technology for their invaluable advice.

Conflict of Interest: The authors have no conflicts of interest to declare.

Author Contributions: Conceptualization: JAL, DHH, SOW, SJK, HJK, DKC, YHC, BRK. Data curation: JAL, DHH, SOW, SJK, HJK, DKC, YHC, BRK. Formal analysis: JAL, DHH. Investigation: JAL, DHH, SOW, SJK, HJK, DKC, BRK. Methodology: JAL, DHH, OHC. Project administration: JAL, DHH. Resources: DHH. Software: JAL, DHH. Supervision: JAL, DHH. Writing – original draft: JAL, DHH. Writing – review & editing: JAL, OHC.