Overall, this large institutional data review found that increasing age and the need for mechanical ventilation during hospitalization were independent risk factors for in-hospital mortality in patients admitted with a primary diagnosis of aspiration pneumonia. Patients older than age 65 were 5 times more likely to die during their admission compared to younger patients. LOS was comparable between the two age groups, most likely due to the higher mortality rate seen in the older patient population.

Out of the 634 patients admitted for aspiration pneumonia from 2008 to 2018, majority of patients (68.1%) were of age 65 or older, with a mean age of 81.7 ± 8.5. The average age of the patients that died during admission was 80.3 ± 13.4. Over the 10-year study period excluding the year 2011, our data have shown that there were at least 1.5 times more cases of aspiration pneumonia requiring admission in those aged 65 or older compared to the younger patients (Fig. 1). We know from existing evidence that the incidence of aspiration pneumonia is higher in the elderly [2]. As the human body undergoes the natural aging process, cerebral atrophy, decreased nerve function, and muscle atrophy can all drastically impact the swallowing function [20]. A case–control study by Almirall et al. showed that oropharyngeal dysphagia significantly increased the risk of pneumonia (OR 11.9) and 92% of patients diagnosed with pneumonia had signs of oropharyngeal dysphagia on video fluroscopic swallowing study (VFSS) [3]. Even in otherwise healthy elders, there are video fluoroscopic and radiological changes in the oral and pharyngeal phases of swallowing when compared to healthy, young adults [21,22,23]. Further, elders’ predisposition to multiple comorbidities puts them at higher risk of aspiration pneumonia [20]. Medical comorbidities such as pulmonary diseases, stroke, dementia, or Parkinson’s disease can devastatingly affect various mechanical aspects of oropharyngeal swallowing, leading to aspiration [5, 24,25,26,27,28]. This trend was observed in our patient population, where those aged 65 or higher had a higher proportion of individuals with two or more comorbidities (88.4% vs 80.2%, p = 0.011) and higher CCI scores (2.0 vs 1.0, p < 0.001) compared to the younger group.

Trend of aspiration pneumonia from 2008 to 2018

When comparing the two dichotomized age groups, elderly patients were less likely to receive mechanical ventilation (14.4 vs. 21.3%; p = 0.038), even when mortality rate was higher in this group (27.8%, p < 0.001) (Table 2). This was an unexpected finding as one would assume a group associated with higher mortality would receive more aggressive and invasive treatments. Previous studies have shown that other factors such as respiratory physiology, burden of comorbidities, and severity of acute illness all contributed to outcomes in mechanical ventilation in the elderly [32, 33]. Therefore age is often a modifier of the effect of disease and not a sole decision altering factor when determining the usage of mechanical ventilation in this population [29]. Further, many elderly patients likely have specific goals of care and therefore “Do Not Resuscitate” orders in this population can further limit intubation and aggressive treatments.

The study has found that SLP involvement was not protective against in-hospital mortality in our study. This may not be surprising because the patients admitted already had aspiration pneumonia and therefore the underlying issues that had led to aspiration were already present. Additionally, given the relatively short LOS of patients admitted for aspiration pneumonia, the full benefit of swallowing rehabilitation may not have been completely elucidated by the current study.

The data for the current study were captured by Decision Support Services, which is a powerful database collecting patient clinical data for care quality improvement and research purposes. We had no missing data for the current study and our unexpected findings will need to be further explored via a larger, more diverse study population from different hospitals regionally and nationally.

The current study demonstrated an alarming in-hospital mortality rate of 27.8% in those over age 65 who were hospitalized with a primary diagnosis of aspiration pneumonia. In 2020, 18% (6.8 million) of the Canadian population was 65 years of age or older [30]. The prevalence of undiagnosed dysphagia in community dwelling elders, a major risk factor for aspiration pneumonia, can be up to 15% [31]. This prevalence increases to 31% in those living in nursing homes [32]. With the increasing aging population in Canada, preventative measures against aspiration pneumonia in the elderly population should become a public health priority. Community programs such as dysphagia screening, including baseline SLP screening, SLP education on oral care, diet modifications, nutrition, as well as dysphagia rehabilitation can help decrease admission to hospital for aspiration pneumonia. Such trends were seen in the United States, incidence of aspiration pneumonia in the elderly population decreased from 40.7 to 30.9 cases per 10,000 people from 2002 to 2012 with implementation of public preventative programs [2, 28, 33]. In-hospital mortality also decreased from 18.9 to 9.8% during the same time period due to reduced disease severity and improved delivery of care to the elderly population [2]. This can not only help prevent admission, but also decrease hospital costs, and ultimately death.

There were several limitations to our study. The inclusion criteria were limited to those with a primary, not secondary, diagnosis of aspiration pneumonia. Primary diagnosis was the label given for the main diagnosis for the patients’ hospital admission. Secondary diagnosis was given when patients developed another disease in addition to the primary diagnosis. Study patients were identified by Decision Support Services at St. Michael’s Hospital using diagnostic codes (ICD-10). Code misclassification is possible in administrative database analysis. Additionally, the ICD-10 code used was J69.0, pneumonitis due to inhalation of food and vomit. This code does not distinguished between whether the aspirant was gastric in origin or oropharyngeal in origin, which may have implications as to whether the aspiration can result in bacterial pneumonia versus chemical pneumonitis. In reality, however, it is very difficult to differentiate the quality of the aspirate and often times a combination of chemical and bacterial aspirates occur [34, 35]. Our patient population was also restricted to one institution in Toronto, which can limit the variability of patient characteristics and treatment preferences. However, our large patient population and completeness of data collection helped mitigate these limitations and our sample size had ample power for analysis. Future work including multiple institutions, patients with secondary diagnosis of aspiration pneumonia while in hospital, as well as incorporating more patient and treatment characteristics will further identify other independent risk factors for treatment outcomes of aspiration pneumonia. A nation-wide database will strengthen the call for dysphagia screening program to prevent aspiration pneumonia and death, particularly in the elderly population.