Obstructive sleep apnea (OSA), a multifactorial disease mediated by multiple genetic, environmental, and developmental factors [1], is highly prevalent and affects an estimated 3% and 9% of women and men, respectively [2]. OSA is associated with a range of medical and social outcomes, such as cardiopulmonary changes, daytime fatigue, irritability, personality changes, and motor vehicle accidents [2,3]. The treatment of OSA often involves the use of nocturnal positive airway pressure (PAP) delivered by continuous PAP (CPAP) devices [4]. A nasal CPAP machine consists of a mask, tubing, and a main body, containing a humidifier and blower motor, and it blows humidified air into the patient’s nose [5]. The National Health Insurance Service (NHIS) in South Korea covers CPAP devices, with one mask and two tubes per year, in patients with OSA. However, standard guidelines for the timing of part replacement or hygiene management of CPAP components are lacking.

Reused instruments, such as nasal steroid spray bottles or nasal irrigation bottles, could be contaminated and may pose an infection risk via the nasal cavity [6,7]. There is a concern that nasal CPAP devices could become contaminated and lead to infections in users. Reports have documented bacterial and fungal colonization on the nasal masks of patients with OSA, yet there have been no cases of associated infections in the upper or lower respiratory tracts [4]. A case of Legionella pneumonia following CPAP device use has been reported [8]. Several studies have attempted to identify microorganisms in CPAP systems; however, no study has disassembled main CPAP units to visually inspect internal contamination.

In this study, we investigated the extent of CPAP device contamination by disassembling systems used daily by patients with OSA and identifying factors that influenced the degree of contamination of each CPAP component.

The research protocol was reviewed in compliance with the Declaration of Helsinki and was approved by the Institutional Review Board of Chung-Ang University Hospital (No. 2312-032-19504), and the requirement for written informed consent was waived.

In total, 55 participants (mean age, 55.38±12.14 years), comprising 44 men and 11 women, were recruited. Fourteen patients had a history of smoking and 27 had been diagnosed with hypertension. Their mean BMI was 26.46±3.13 kg/m², and the mean AHI was 42.53±22.12. The mean total CPAP usage duration was 932.23±418.50 days, and the mean daily usage duration was 4.93±1.53 hours. The mean values for the degree of contamination of the mask, tube, and filter were 2.94±1.56, 2.60±1.35, and 3.05±2.15, respectively (Table 1). During the complete disassembly and cleaning of the CPAP device, we found that not only the mask and tube, which are easily observed and regularly replaced, but also the interior body and humidifier of the CPAP devices were considerably contaminated (Fig. 1). The mean values for the degree of contamination of the humidifier, interior, and exterior main body were 3.83±2.27, 3.90±2.29, and 3.47±1.68, respectively (Table 1).

We fitted multivariate regression models with independent variables for contamination of the mask, tube, humidifier, interior, and exterior of the main body. Age and AHI were selected as predictors of mask contamination and were statistically significant (P=0.020 for age, P=0.033 for AHI, R²=0.122). The model for tube contamination included only the total usage duration of CPAP as a predictor; however, the coefficients of the selected variables were not statistically significant (R²=0.041). The humidifier contamination model included age and BMI as explanatory variables, and only age emerged as statistically significant (P=0.049, R²=0.093). The model for contamination of the interior of the main body included the total usage duration of CPAP, age, and BMI as explanatory variables, of which age (P=0.020) and BMI (P=0.033) were statistically significant (R²=0.162). For the contamination of the exterior main body, the model considered the total usage duration of the CPAP, age, AHI, and BMI as predictors, of which only age showed statistical significance (P= 0.024, R²=0.176). To summarize, age was statistically significant in the models for contamination of the mask, humidifier, and both interior and exterior main bodies (Table 2).

For further subgroup analysis, we categorized the data on the degree of contamination of the mask and tube according to mask usage duration (≤1 year or >1 year) and tube usage duration (≤6 months or >6 months). For mask contamination, when the mask usage duration was ≤1 year, no variables were fitted to the model. However, when the duration of mask usage was >1 year, age was selected as an explanatory variable and showed statistical significance (P=0.050, R2 =0.265) (Table 3). For the contamination of the tube, when the usage duration was ≤6 months, tube usage duration, sex, BMI, total usage duration of the CPAP device, and average daily usage duration were selected as variables. The tube usage duration (P=0.023) and the average daily usage duration of the CPAP device (P=0.014) showed statistical significance, with the tube usage duration having a negative coefficient. This indicated that, as the duration of usage increased, the degree of contamination decreased (R²=0.624). When the usage duration exceeded 6 months, age, sex, and total duration of usage were selected as variables for tube contamination; however, none of these were statistically significant (R²=0.271) (Table 3).

Finally, we evaluated the correlations between the degree of contamination of the mask, tube, humidifier, interior, and exterior of the main body. Most variables exhibited high correlations of ≥0.7, with a notably higher correlation between the degree of the contamination of the humidifier and exterior main body (correlation coefficient, 0.908) (Fig. 2).

The primary finding of this study was that, despite adhering to the NHIS guidelines, regularly replacing the patients’ masks, and monitoring for proper hygiene management of the CPAP device, a significant level of contamination was visually observed (Fig. 1). The duration of usage was not extensively associated with the degree of contamination of the various CPAP components. A significant correlation was not found between the duration of usage and the level of contamination of the mask and tube, as these parts were regularly replaced in accordance with the national NHIS guidelines. Instead, when we further evaluated the relationship according to the duration of usage of the mask and tube, a negative association was found between the duration of usage of the tube and the degree of tube contamination in cases where the duration was ≤6 months (Table 3). While we cannot provide a conclusive explanation for this, it may be that the visible increase in tube contamination prompted more diligent cleaning by patients. These findings could indirectly suggest that the current our own guidelines for tube replacement every 6 months may be too infrequent, and a shorter replacement interval should be considered. Moreover, the total usage duration of CPAP and the average daily usage duration showed no significant correlations with the degree of humidifier contamination in the interior or exterior of the main body (Table 2). Instead, we found that age was the most consistently associated factor, as it demonstrated statistically significant relationships with the degree of contamination of the mask, humidifier, and interior and exterior of the main body. We hypothesized that elderly patients may be less accustomed to directly handling machinery than younger individuals, potentially leading to a passive approach to hygiene management. Other characteristics, such as the AHI and BMI, were significantly associated with contamination of the mask and the interior of the main body. Therefore, we suggest that clinical characteristics—including, most notably, age—should be considered along with the usage duration for the establishment of guidelines on the hygiene management of CPAP devices and for patient education.

The second finding of the current study was that the humidifier and the internal components of the CPAP device, which are not visible without disassembly and cleaning, may be more prone to contamination than the external parts, such as masks or tubes. The average level of contamination in the humidifier and the interior of the main unit was greater than that found in the mask and filter, suggesting a poor level of hygiene (Table 1). In this country, healthcare is administered through the NHIS, yet there are no specific guidelines for when to replace the humidifier or internal parts of CPAP machines. Therefore, we recommend the development of guidelines for the replacement or regular cleaning of the CPAP device’s internal components, in addition to the masks and tubes.

Finally, the degree of contamination of the parts of CPAP devices showed significant correlations. In particular, the degree of contamination of the humidifier and interior of the main body, which could not be easily accessed by patients, was significantly correlated with the degree of external device contamination (Fig. 2). Therefore, we suggest that the internal compartment of the CPAP device should be checked to determine whether the external part of the CPAP device is contaminated.

The relationship between the cleanliness of CPAP devices and the incidence of inflammatory diseases in patients remains unclear. Given that CPAP is used daily by individuals with OSA and that most of its accessories are designed for repeated use, it is reasonable to suspect that various components of the CPAP system could harbor a range of microorganisms. Christopher et al. explored the possibility of bacterial colonization in CPAP water reservoirs and its potential link to the development of chronic rhinosinusitis (CRS). They hypothesized that air delivered through the CPAP machine could carry pathogenic agents into the patient’s airways. Their findings, however, indicated that even though some atypical bacteria were present in the CPAP reservoir, a positive culture did not correlate with an increase in CRS symptoms [5]. Additionally, no heightened infection risk has been associated with the use of reprocessed CPAP devices when compared to new ones, according to a study involving 120 CPAP devices [9]. In contrast, the rate of infectious diseases was found to be 25% among OSA patients who did not use CPAP, compared to 43% among those who did. Notably, CPAP users who utilized humidifiers experienced a higher incidence of upper airway infections [10]. A recent study employing 16S rRNA gene sequencing to assess the nasal microbiome revealed that CPAP treatment did not result in longitudinal changes in nasal microbiota, with no significant alterations in either α- or β-diversity.

Nasal CPAP is predominantly a home-based treatment for OSA patients. Therefore, maintaining hygiene protocols for CPAP devices presents a significant challenge and necessitates careful consideration. We recommend that additional research be conducted, including 16S rRNA gene sequencing of both CPAP devices and their users, as well as large-scale population-based epidemiological studies.

The current study had some limitations. First, the contamination level was measured subjectively. Although we attempted to locate an objective assessment metric for contamination, we were unable to find one. We suggest that there is a need for objective measurement indicators, beyond specialized methods such as microbial identification, that patients can use to assess contamination levels. In this context, we suggest that it is necessary to establish guidelines for the periodic inspection of the components of CPAP devices and their corresponding maintenance methods. Second, the number of enrolled participants was relatively small. As the disassembly and cleaning service of the CPAP device was provided free of charge by skilled technicians, only a limited number of participants could be recruited. We are continuing this disassembly and clearing service and plan to conduct further studies with a larger dataset. Third, the clinical characteristics of the participants in this study were not evenly distributed. In particular, most participants in this study were men. Although the percentage of female patients with OSA is not high, an additional study on the effect of clinical characteristics, including age, sex, and concurrent medical diseases, should be considered [11]. We could not rule out the possibility that environmental variables, such as humidity and temperature, in which the CPAP devices were daily applied could affect the results. Furthermore, we hypothesize that patient compliance with CPAP maintenance also could influence the contamination level. Finally, this study had a cross-sectional design, and it was not possible to evaluate changes in contamination over time. Therefore, further large population-based observational studies that consider various characteristics are needed to provide confirmative results.

We found that many parts of CPAP devices, including the humidifier and the interior and exterior of the main body, showed considerable levels of contamination. The duration of usage was not uniformly associated with the degree of contamination; among the characteristics that were evaluated, age was most consistently associated with the degree of contamination of CPAP components. We suggest that age-specific guidelines for the hygiene management of components, besides the masks and tubes, of CPAP devices should be prepared.