The purpose of the present study was to clarify differences in infection characteristics between patients hospitalized with OI or another bacterial ONP infection. The specific aim was to evaluate clinical infection variables and infection severity according to infection aetiology and to clarify the features of OIs. A quarter of all ONP infections were OIs (Fig. 1), and dental origin was the second most common aetiology after pharyngeal region infections. The hypothesis was that OIs have special features that differ from other ONP infections, and this was confirmed. Hospitalized patients with OI more often had restricted mouth opening, redness of the facial skin, and facial or neck swelling (or both). LHOS was significantly longer in patients with OI (Fig. 2) and significantly more often required ICU care (Table 3) than ONPs. Thus, OIs are a clinically notable cause for hospitalization when all ONP infections are considered.

The spectrum of symptoms and findings in ONP infections is wide given the differences in aetiology. Features reported most often include dysphagia, fever, malaise, odynophagia, ipsilateral otalgia, severe sore throat, cervical lymphadenitis, trismus, and swelling of neck, face, tongue base, and oral cavity [6, 12,13,14]. Previously, studies that clarified features of different ONP infections focused mainly on life-threatening conditions, such mediastinitis, necrotizing fasciitis, and Lemierre’s syndrome [15]. For example, mediastinal spread occurs more commonly in non-odontogenic deep-neck infections [8, 16] than those of dental origin. The present study focused more widely on clinical findings at the time of hospital admission. Typical features of OIs were restricted mouth opening, redness of facial skin, and facial or neck swelling (or both). Thus, it is essential to consider odontogenic aetiology if these findings occur, to achieve optimal treatment. OIs are almost always treated by surgical intervention, which includes abscess drainage and removal of the focus tooth.

In contrast to previous studies focused on hospital stay [6, 12], patients with OIs had longer LHOS than patients with other ONPs. We compared OIs to all bacterial infections of ONP region, which may be responsible for this difference. However, OIs more often required ICU treatment, as 75% of all patients that were treated in ICU had an OI. Airway management and mechanical ventilation were the main reasons for ICU treatment. However, 6 patients with epiglottitis received tracheostomy and were treated at the ward. Thus, ICU care for treatment of a compromised airway may influence the results. On the other hand, the entire LHOS was significantly longer in OI patients. It should be emphasized that the need for hospital care and most OIs in general can be prevented by improving preventive care (i.e., regular dental care and effective treatment of an incipient infection). In addition, there should be a greater emphasis on earlier identification of these infections, as both medical and dental professionals have difficulties in detecting OIs [17].

A peritonsillar abscess is the most common otorhinolaryngological infection requiring hospitalization [18]. The annual incidence of peritonsillar abscess is 9/100000/y [19]. Overall, oropharyngeal infections, including peritonsillar infections, were the most common infections of all hospitalized patients according to our results. However, only 5 of these required prolonged intubations. Patient characteristics and clinical findings differed when compared with OIs. Patients in this group were younger than those with OIs (mean 42 years, median 38 years), had on average slightly higher infection parameters, and more often had difficulty swallowing. On the other hand, patients with OIs more often had facial swelling, restricted mouth opening, and redness of the skin. Respiratory difficulties also occurred more often among patients with OIs. Our results may assist clinicians in differential diagnostics between OIs. Patients with infections of the oropharyngeal region should be referred to the most suitable treatment facility.

Among other ONP infections, epiglottitis was the third most common group in this study. Acute epiglottitis in adults have similar symptoms as other ONP infections [20]. The dominant symptom in our study was swallowing difficulty (observed in two-thirds of epiglottitis patients), which is an essential sign of dyspnoea with laryngeal oedema, which may lead to sudden upper-airway obstruction [15, 21]. All other clinical parameters in epiglottitis patients were clearly more uncommon. Infections that originate from salivary stone and obstruction and other conditions on the mucosal surface of the upper aerodigestive track can also lead to hospitalization and severe infections. However, the present study showed that these aetiologies are rare, especially when considering the need for ICU care. Only one infected mandibular fracture and tongue abscess required ICU care. The remaining patients all had OIs, epiglottitis, or peritonsillar or parapharyngeal abscesses.

The limited accuracy of some variables and particularly clinical findings may be due to the retrospective study design. Additionally, the number of patients in rarer ONP subgroups remained low; thus, detailed analyses for these infection types were not conducted. A prospective study design would be beneficial to clarify differential diagnostics in more detail.