Table 2.

Characteristics of included studies

No.	Author country, year	Study design	Objectives	Participants	Participants/controls	Diagnosis of pneumonia	Diagnosis of aspiration/dysphagia	Conclusion
1	Katsura [20]. Japan, 1998	Retrospective	Outcomes in patients with recurrent pulmonary aspiration	Hospitalized older persons with repeated aspiration events (≥ 1/week)	38/0	Symptoms (fever, cough, sputum), inflammatory markers	Witnessed aspiration during eating and requiring intervention such as suction	1. Repeated aspiration mostly occurs with underlying diseases of CVD, dementia, and deterioration of ADLs; 2. Prognosis is poor; PEG contributes to survival but does not prevent pneumonia
2	Tokuyasu [21]. Japan, 2009	Prospective cohort	1. Causative organisms of AP (bronchoscopy), 2. Efficacy of meropenem for AP	Hospitalized patients (≥ 75 yo) with AP	62/0	Symptoms (fever, cough, purulent sputum), blood tests, lung infiltration on X-ray and CT	1:aspirated content detected in respiratory tract, 2:coughing or choking before/during/or after swallowing, and 3:dysphaagia on videofluoroscopy	1. Anaerobic bacteria coverage may be necessary for potentially fatal AP; 2.Meropenem is effective and tolerable
3	Takenaka [22]. Japan, 2011	Prospective cohort	Factors related to repetitive AP in older persons with dysphagia	Admissions for AP ≥ 2 times during study period (control: admitted once)	15/53	Symptoms suggesting respiratory infection, inflammatory markers, and X-ray	Symptoms suggesting aspiration prior to admission	The relapse group had higher rates of coming from institutions or hospitals, and higher brain dysfunction
4	Bosch [23]. Spain, 2012	Prospective cohort	Mortality rate and prognostic factors in old patients with dementia, hospitalized for AP	≥ 75 yo admissions with AP with dementia	120/0	Chest infiltration and 1 major criteria (cough, sputum, BT ≥ 37.8°) or 2 minor criteria (dyspnoea, pleuritic pain, delirium, RR > 20, consolidation, WBC > 12,000/µL)	Risk factors for oropharyngeal aspiration and a history of witness or suspected aspiration	In-hospital and 6 month mortality were high (33.3%, 50.8%). Multilobar involvement and lower lymphocyte counts were associated with hospital mortality, and older age, greater dependence and malnutrition with 6 month mortality
5	Komiya [24]. Japan, 2013	Retrospective	CT features of AP	Admissions for pneumonia who were subsequently confirmed to have dysphagia by VF	53/0	Not mentioned	On VF: disability to move food or liquid from the mouth through the pharynx and oesophagus into the stomach safely and efficiently	Common patterns were bronchopneumonia and bronchiolitis pattern. Distribution was characterized by gravity dependence
6	Pinargote [25]. Spain, 2015	Prospective cohort	Clinical features and outcomes of AP and non-AP	≥ 80 yo admitted with AP (control: non-AP)	46/30	Radiographic evidence of pulmonary infiltration and acute onset of symptoms of LRTI	Infiltration in posterior segments of upper lobes or apical/basal segments of lower lobes and vomiting or witnessed aspiration, or risks for aspiration (dementia, CVD, NMD, pharyngolaryngeal dysfunction, oesophageal dysfunction or mechanical obstruction, tube feeding, gastroesophageal reflux, or poor swallowing previously confirmed)	AP showed higher levels of sodium, low estimated glomerular filtrate rate, higher severity of pneumonia, and slightly higher mortality than non-AP
7	Palacios-Cena [26]. Spain, 2017	Retrospective	1. AP hospitalizations according to sex and comorbidities, 2. Time trends in outcomes, 3. Factors associated with in-hospital mortality	≥ 75 yo admitted and with a primary diagnosis of AP according to ICD-9-CM (using national database)	111,319/0	Not mentioned	AP event codes according to the ICD-9-CM: 507.x (pneumonitis or pneumonia caused by inhalation of vomitus or food)	AP patients were older, more male, and had more comorbidities. Over time, length of hospital stay and in-hospital mortality decreased in both sexes, but readmissions increased significantly in females
8	Nakashima [27]. Japan, 2018	Prospective cohort	Association of silent aspiration and mortality in AP	≥ 65 yo admitted for AP (2 acute hospitals, Japan)	170/0	New gravity-dependent shadow on chest X-ray/CT, and ≥ 2 of the following: BT ≥ 37.5 °C, high CRP, WBC ≥ 9000/µL, purulent sputum	Positive water swallowing test or condition related to aspiration (neurological disorder, bedridden, severe cognitive impairment or gastroesophageal reflux)	Silent aspiration detected on cough latency test can predict 1-month mortality in older AP
9	Manabe [28]. Japan, 2020	Retrospective	Factors to distinguish AP from CAP in primary care	AP in primary care database of 20 hospitals and clinics (control: CAP)	130/58	Not mentioned	Overall clinical assessment, risk factors for aspiration, and/or chest radiograph abnormalities	Characteristic factors for diagnosing AP in the oldest-old in primary care settings are: nursing home and dysphagia risks (cerebral infarction, dementia, hypertension)

yo years-old, CVD cerebrovascular disease, ADL activities of daily life, PEG percutaneous endoscopic gastrostomy, AP aspiration pneumonia, BT body temperature, RR respiratory rate, WBC white blood cells, CT computed tomography, VF videofluoroscopy, NMD neuromuscular disease, CAP community-acquired pneumonia