Aspiration pneumonia (AsP) is a lung infection induced by pathogens and materials from the mouth and stomach, and the risk is generally high in older adults [1
]. The development of AsP is a socio-clinical burden, and identifying and understanding AsP is getting crucial in rapidly aging societies, like Japan [1
AsP is recognized as a phenotype of community-acquired pneumonia (CAP), and several studies have indicated that 7–24% of cases of CAP are due to aspiration [5
]. A Japanese multicenter prospective study reported that approximately 60% of hospitalized patients with CAP were diagnosed with AsP [7
]. AsP is more severe than non-aspiration pneumonia [4
], with higher rates of mortality and recurrence as well as increased lengths of hospital stay compared with CAP [3
]. In some cases, AsP can prompt the development of necrotizing pneumonia and/or lung abscess, leading to a prolonged course of antibiotics and surgery [9
]. These findings underscore the importance of managing AsP compared with CAP.
The diagnosis of pneumonia is generally troublesome, especially in older adults [10
]. The standard criteria for a diagnosis of pneumonia are the presence of acute respiratory symptoms and fever associated with newly identified and modified infiltrates on chest radiography [11
]. Among older adults, however, the clinical symptoms and signs of pneumonia are atypical, and chest radiography abnormalities can be non-specific [13
]. To make the diagnostic criteria of AsP and the preventative measures to stop its recurrence is an issue among older adults [17
In the primary-care settings, oldest-old patients with AsP are often seen by primary care physicians and general practitioners [18
]. Pneumonia, including AsP, appears in the long-term care as provided in nursing homes, and the patients also visit medical facilities, which is an issue for caregivers [19
]. Clinically diagnostic markers to determine AsP in such settings have not yet to be elucidated; therefore, the present study aimed to clarify the characteristic factors for distinguishing AsP from CAP in primary-care settings in Japan.
The present study examining oldest-old adults with pneumonia in the primary-care settings revealed that living in a nursing home and having comorbidities with risks of dysphagia, such as cerebral infarction and dementia, were preferentially characteristic factors that could distinguish AsP from CAP. Hypertension had a negative association with the diagnosis of AsP. As there have been few studies of clinical markers to determine AsP for oldest-old adults, the findings will aid in the management of AsP in such adults with suspected pneumonia.
Living in a nursing home can be a situation that is associated with the development of AsP [2
], as such homes provide nursing care for geriatric syndrome and other disabilities. It is also important to note that pneumonia among patients who live in a nursing home is considered nursing- and healthcare-associated pneumonia (NHCAP), mainly being caused by drug-resistant bacteria [24
]. Patients with NHCAP are typically older and show a poorer prognosis than those with CAP [26
]. In the present study, the data of bacteriological tests, including the assessment of drug-resistant pathogens, were unavailable, so an etiological approach will be necessary to prevent recurrent pneumonia, such as AsP [27
In the present study, dementia and cerebral infarction were found to be factors associated with AsP. Risk factors for aspiration are recognized to include an impaired consciousness, weakness, and swallowing dysfunction [2
]. Dysphagia frequently occurs as the result of cerebral vascular disease and/or degenerative diseases of the cerebral nervous system, including dementia [28
]. A study reported that patients with silent cerebral infarction had a higher risk of developing pneumonia than those with normal findings of head computed tomography [29
]. A study examining patients living in a geriatric facility also suggested dementia as a risk factor for the development of AsP [30
]. These can partly support the results of the present study.
To narrow down the characteristic factors among many variables with potential collinearity, a stepwise logistic regression analysis was used to extract the variables in the present study. The selection of the variables was reasonable in the methodology; however, this method could have been too strict, and real-world unselected information might also contribute to clinical practice. Therefore, some clinical information characterized by comparative statistics (i.e., an older age and low body temperature, heart rate, and diastolic blood pressure, as well as witnessed meal dysphagia) may aid in the management of AsP and help families and caregivers prevent AsP.
AsP involves misdirection of the oropharyngeal or gastric contents into the larynx and lower respiratory tract, and the aspiration of oropharyngeal secretions increases with age [2
]. When primary care physicians and general practitioners vaguely think that AsP develops equally (regardless of age) among older adults, it may be of value to suggest that the risk of AsP can still increase with age even among oldest-old adults.
On the other hand, physical functions are seemingly relevant indicators related to aging rather than chronological age among older people [31
]. Regarding the physical manifestations, the body temperature, heart rate, and diastolic blood pressure in patients with AsP could be lower than in patients with CAP. It is usable to focus attention on these manifestations for AsP, as primary care physicians and general practitioners tend to rely on the physical manifestations in daily practice. A fever is often absent in older adults with pneumonia; consequently, the heart rate does not increase [9
]. In previous studies, the systolic heart function did not decrease with age [33
], whereas the diastolic ability did decrease [34
]. A low blood pressure is used as a marker in CURB-65 and A-DROP, which are the pneumonia severity indexes recommended by the British Thoracic Society [36
] and the Japanese Respiratory Society [12
], respectively. Lowering blood pressure as late-life physical dynamics indicates a potentially poor health with comorbidities [37
]. This earlier knowledge may be associated with our present findings that hypertension was a negative factor of AsP in the logistic regression analysis and a low diastolic blood pressure appeared in AsP. The physical manifestations are thus indicative to be carefully evaluated in order to aptly manage AsP. Aging-prone pathophysiology more observed in older adults with AsP than those with CAP may merit further research. A comparison of the physical manifestations in those with AsP to healthy older people might be needed.
Aspiration is generally not witnessed, and even healthy people passively aspirate oropharyngeal secretions while asleep at night [39
]. However, in the present study, witnessed meal dysphagia was reported by family members and caregivers in patients with AsP, whereas meal dysphagia was not reported for any patients with CAP. Meal dysphagia is influenced by a decreased food bolus-forming ability [41
]. Insufficient food-bolus formation and chewing owing to missing teeth, as well as deterioration in tongue movements, increase the risk of aspiration [41
]. In Japan, older adults who live in nursing homes receive 24-h supervision by caregivers. Particularly during mealtimes, caregivers carefully watch older adults or help them to eat. On the other hand, community-dwelling older adults living at home may eat meals alone during the daytime more often than residents in nursing homes. Paying close attention to older adults during meals is suggested to be useful for the prevention and early detection of meal aspiration leading to AsP.
Several limitations associated with the present study warrant mention. This study used the comparative design by cases extracted from the dataset. While the set was made using real-world data, the study might include information bias, as the preconception by study investigators when the diagnosis was not blinded. The variables of the database were not always similarly formatted for all patients and those with pneumonia. For example, although having gastro-esophageal reflux, a risk factor of AsP, was not detected in the study, this might simply have been due—at least in part—to the unformatted collection of data. Furthermore, the laboratory, bacteriological, and chest radiographic findings were not always recorded in all patients. Indeed, even though chest radiography was not performed in the study sites of the primary-care physicians and general practitioners who first diagnosed the patients, the diagnosis of pneumonia was confirmed in referred/hospitalized hospitals using radiography in all patients with AsP and CAP, following the guidelines [12
]. However, a previous study indicated that the detection failure rate of chest radiographs was approximately 30% among patients with NHCAP [44
], underscoring the importance of considering patients’ overall characteristics in the diagnosis of pneumonia. Given these limitations, further investigations with a well-formatted prospective design will be required to confirm the present findings.
In conclusion, among oldest-old adults in the primary-care setting, it is relevant to know their living situation (e.g., in a nursing home) and the presence of underlying diseases with risks of dysphagia (e.g., cerebral infarction and dementia) to diagnose AsP. Some clinical information (i.e., an older age and low body temperature, heart rate, and diastolic blood pressure, as well as witnessed meal dysphagia) may also aid in the management of AsP and help families and caregivers prevent AsP. As societies around the world age, these findings should be further investigated to aid in the management of pneumonia among oldest-old adults in the primary-care settings.