Infections of the oral and maxillofacial region have a high incidence and can cause severe complications (1–3), such as mediastinitis, airway obstruction or sepsis (4, 5).

Odontogenic infections are the most common cause of oral and maxillofacial abscesses (2, 6–8).

Several general and local predisposing factors are known to increase the risk of severe odontogenic infections. These include for example unstable diabetes mellitus (DM), immunosuppression, history of radiation and/or chemotherapy (9–21).

Orofacial odontogenic infections are frequently mixed aerobic and anaerobic infections (6, 22). The bacterial spectrum is diverse, and the microbiology result often excogitates the existence of commensal oral flora (6, 23).

Treatment of odontogenic infection is based on surgical drainage, focus remediation and antibiotic therapy (6, 24, 25). However, if the abscess is treated incorrectly or late, the infection may spread in deeper facial spaces, where it becomes difficult to treat and may be fatal (26–29). In addition to surgery, the choice of empirical antibiotics is also critical (26, 30). Widespread indifferent use of antibiotics has led to the emergence of resistant bacteria (31).

According to the joint definition of the German Society of Geriatric Medicine (DGG), the German Society of Gerontology and Geriatrics (DGGG), the Federal Association of Clinical geriatric Institutions (BAG) and the Professional Association of German Internists Section geriatrics, the geriatric patient is characterised by advanced age, mostly 70 years and older, combined with a geriatric–typical multimorbidity (32–34). Elderly patients are considered high-risk patients with a higher probability of prolonged hospitalisation (33, 35).

Odontogenic infections affect people of all ages (28). However, age-associated decline in reserve and function may reduce the ability to cope with acute external stressors, typically defined as frailty (36, 37). Frailty is associated with a higher risk of poor outcomes such as disability and mortality (38). Inflammation may be closely associated with frailty (39). In the elderly, their reduced immunological reaction and comorbidities may be associated with an increase in severe infections (40). In addition, diagnosis and treatment of odontogenic infections in the elderly may be more complex than in younger patients because of more comorbid conditions (41).

The number of individuals aged 60 and over worldwide is expected to increase to more than 2 billion by 2050 (42).

Thus, there will be more elderly patients with oral and maxillofacial infections (1). Only a few studies consider age as an important factor in head and neck infections, but without specification in odontogenic infections (1, 3).

We aimed to analyse the differences in clinical features, treatment modalities, and bacterial analysis of odontogenic infections between elderly and non-elderly patients. We hypothesise that we will identify variables associated with worse outcome to improve the clinical risk stratification of elderly patients.

The mean age of all patients in our study was 50.0 ± 19.9 years, similar to other studies (7, 44, 45). Also similarly, the incidence of deep neck infections was higher in the elderly (41, 44, 46).

Equal to other studies, males were predominant (53.2%), with a ratio of 1,13:1 (10, 47–49),. In the present study, older patients were predominantly female (54.2%), similar to the study of Chi et al. (41), but in contrast to the findings by Zheng et al. (1).

We found a significant association between CRF and complications. Furthermore, regression analysis showed that CRF was the strongest predictor for complications and a prolonged LOS.

Patients with CRF, especially in end-stage renal diseases (ESRD), have been reported to have a higher risk of infectious complications (50, 51) due to multifactorial mechanisms such as neutrophil dysfunction, uremic toxicity, biological incompatibility, anaemia, iron overload and a dialysis access and procedure (52–54). As described by Dalrymple et al., infection is the second leading cause of death in patients with an ESRD (54). The authors also found that patients with CRF have longer LOS for infection-related admissions than those without (54, 55).

Several factors such as advanced age, high burden of co-morbidities, hypoalbuminemia (56, 57), immunosuppressive therapy (58), nephrotic syndrome (59), uraemia, anaemia or malnutrition (60, 61) may additionally increase the risk of infection in patients with CRF.

We identified two studies that investigated ESRD in relation to head and neck infections.

Chang et al. found a higher incidence rate and cumulative incidence in patients with ESRD than in those without. They also described a higher mortality rate and poor survival in patients with ESRD, although LOS was not significantly longer (62). A limitation is that only a quarter of patients underwent surgical treatment, whereas in our study all patients did. Another limitation is the definition of ESRD. Chang et al. defined the target group based on ESRD-related ICD-9 without specific GFR, whereas our study defined CRF as GFR < 30 ml/min (62).

Tsai et al. reported that patients with deep neck infections and ESRD had a significantly longer LOS, more ICU admissions and a higher mortality rate than patients without. They also found a higher incidence of methicillin-resistant Staphylococcus aureus (MRSA) in the ERSD group, which was not investigated in this study (63).

Regarding the top, the studies by Chang et al. and Tsai et al. looked at all types of deep neck infections without specifying odontogenic origin. However, Chang et al. mentioned the odontogenic origin as the most common cause of head and neck infections (62).

Both studies examined the age of the patients in a subanalysis. Tsai et al. described a higher incidence of ESRD in patients younger than 65 years, whereas Chang et al. described no difference between those younger and older than 65 years (62, 63). Both findings contrast with our study, in which older patients had a significantly higher incidence of CRF than non-elderly patients.

Many studies also reported an association between DM and a complicated course of treatment for head and neck infections up to life—threatening complications (11, 64–66).

However, we found no significant correlations between DM and complications or prolonged LOS.

In this study, the most common site of infection in all patients was the peri/submandibular space, which is similar to many other studies (18, 19, 49, 66).

Contrary to the expected accelerated spreading of the infection in compromised elderly patients, these group had significantly more infections in the paramandibular/vestibular, fossa canina or maxillary spaces. Since the study excluded outpatients, we suspect that the number of younger patients with infections in this space may not necessarily be lower but was not included the analysis due to the criteria.

Flynn et al. described these cavities as “low-risk spaces”, with a low incidence of complications (67). Nevertheless, these patients were admitted to the hospital in the present study. We hypothesise that hospitalisation was due to pre-existing systemic disease and possible concomitant (anticoagulant) medication.

Chi et al. reported the parapharyngeal cavity as the most affected space, in older as well as in younger patients with a cut-off age of 65 years. However, this study also included non—odontogenic causes (41).

The lower molar was the most common focus of infection, which is consistent with many other studies (19, 22, 44, 49, 68, 69). Particularly in younger patients, the lower molars were by far the most common focus (51.2%), resulting in many infections in the submandibular space.

In older patients, the distribution of the odontogenic focus was more even. Since the apex of the tooth of origin determines the path of dissemination (22), the results are consistent with the distribution of infection space in the older group.

In our study, infections at the base of the mouth (OR:2.88; p < 0.001) and in the parapharyngeal cavity (OR:3.50; p < 0.001) lead to significantly more complications. In older patients, infections in the peri/submandibular space significantly increase the likelihood of complications (OR:3.51; p = 0.006).

In addition, infections in the lower molars lead to a significantly higher risk of complications (OR:1.72, p = 0.011). These results are in line with the studies of Alotaibi et al. and Ylijoki et al. (9, 10).

Due to modern diagnostics and therapy, serious complications after odontogenic infection have a low incidence and mainly occur in the presence of predisposing factors (14, 19, 70).

In our study 97 patients (8.3%) experienced complications, the most commonly of which were ICU admission (5.1%) mainly for upper airway obstruction (3.2%). The percentage of patients requiring ICU admission was lower than previously reported (18, 66, 71, 72). For example, Barber et al. described a percentage of 21.4% requiring ICU admission, with no significant difference in age (21). Gams et al. even reported an incidence of ICU admission up to 45% (66).

Severe odontogenic infections are known to cause upper airway obstruction (1, 8). Adovica et al. reported a complication rate of 11.4%, mainly caused by upper airway obstruction (18). Suehara et al. even reported a complication rate of 50.3%, mainly caused by airway compromise (72).

As widely expected, and in conclusion with our results, the risk of upper airway obstruction depends on the infection space which in turn often depends on the dental origin. Branstetter et al. described the “mylohyoid line” as a significant border in the communication between the mouth base or sublingual space and the submandibular space of the neck. Furthermore, they described that infections with their dental origin in the anterior part of the mandible first affect the sublingual space, whereas infections from the second or third molar can directly spread into the deeper lodges (73). Nevertheless, both spaces communicate via the unattached posterior margin of the mylohyoid muscle (74).

One possible explanation for this quantitative difference in complications and upper airway obstruction is the inclusion of infection sites in some study analyses. For example, infections in the submandibular and parapharyngeal spaces are much more common and require intubation and intensive care therapy to protect the airway.

In this study, 38 patients (3.2%) underwent a second operation to drain all collections, which is consistent with the findings of Gholami et al. (69). The rate was higher in the elderly (5.0%) compared to the non-elderly (2.8%), but not significantly different. Adovica et al. reported a significantly higher reoperation rate in elderly patients compared to younger patients (18).

In the present study the rate of complications was slightly higher in older patients (9.6% vs. 7.9%), but the difference was not significant. Similarly, regression analysis didn't show a significant effect of age on complications. This contrasts with other studies. Zhang et al. reported a higher incidence of life-threatening complications in patients over 65 years of age. The average age of patients with life-threatening complications was 9.6 years higher than those without (7). Adovica et al. describe a higher complication rate, ICU admission and LOS in older patients compared to younger patients, but without precise information on the age structure (18). In addition, Suehara et al. reported age as s significant variable associated with complications (72).

Furthermore, when looking at the subgroups, the incidence of ICU therapy and upper airway obstruction was higher in younger patients. In addition, Riekert et al. also described, that age was not significantly correlated with an ICU admission (75).

LOS is widely accepted as a surrogate marker of complicated course and adverse outcome in hospitalised patients (76, 77).

The mean LOS in our study was 3.92(3) ± 2.69 days, which was shorter than in other studies (10, 14, 66), but within the range of 3–10 days reported in previous studies (25, 30, 48, 68, 71, 78, 79). Park et al. reported a mean LOS of 12.43 days (44), Suehara et al. of 12.6 ± 14.4 days (72) and Seppänen et al. even reported a mean LOS of 14.8 days; however they only included 35 patients (14).

In our study, age as an isolated risk factor was associated with a longer LOS, but the difference was not significant (p = 0.129). Regression analysis showed a weak association between age and longer LOS (p = 0.001).

Wang et al. reported that older patients had a significantly longer LOS (80). Gams et al. described age as a significant predictor of longer LOS (66).

Park et al. identified age as a predictor for a LOS longer than 12 days. Among the other risk factors, age had the highest ratio for a longer LOS (44).

Regression analysis showed a significant association between peri/submandibular, parapharyngeal and oral base infections and prolonged LOS (p < 0.05). In older patients, the regression coefficient increased in all areas. As a result, we saw a stronger association between older patients with infections in these areas and prolonged LOS (p < 0.05). In contrast, Flynn at el. didn't find a significant association between prolonged LOS and involvement of the specific deep fascial spaces (67).

We also observed a significant association between lower molar infection and longer LOS, which also increased in the older population. In line with this, Alotaibi et al. described a longer LOS in patients with mandibular odontogenic infections compared to those with maxillary odontogenic infections (10).

In our study, regression analysis showed, that WBC and CRP levels on admission were positively correlated with LOS (p < 0.001 and complications (p < 0.001). Park et al. also described a CRP level > 10 mg/dl as a risk factor for prolonged LOS (44).

Flynn et al. described the WBC level as a significant predictor of reoperation and prolonged LOS (67). Mathew et al. reported a WBC count greater than 15 × 10⁹/L as a risk factor for life-threatening complications (11).

Many other studies have also shown that CRP levels can be a valuable marker for determining the severity of an odontogenic infections (9, 75, 76, 81–83). Sharma et al. reported a strong correlation between CRP levels and the severity of infection (81).

Ylijoki et al. and Riekert et al. reported a significantly higher WBC and CRP levels on admission in patients requiring intensive care compared to those not requiring intensive care (9, 75).

Riekert et al. conclude that higher CRP levels appear to be associated with the severity of deep cavity infections of odontogenic origin (75).

Regression analysis showed a significant correlation between higher WBC and CRP levels and complications as well as prolonged LOS, which is consistent with the findings of Gholami et al. (69). Wang et al. reported a CRP level > 100 µg/ml as a significant predictor of prolonged LOS, whereas a WBC level > 15,000/mm³ was not significantly associated with LOS (80). Consistent with this, Stathopoulos et al. also confirmed the CRP level as the only significant predictor of prolonged LOS.

Regarding the multivariate regression analysis, only higher CRP levels had a significant correlation with prolonged LOS (p < 0.001) and complications (p < 0.001). Therefore, we suggest that CRP is the most predictable laboratory marker of complicated courses in the elderly.

The three most frequency isolated bacteria by culture-based methods in this study were members of the Streptococcus anginosus group, Prevotella spp. and CNS, similar to the findings of Gams et al. (66) and other authors (78, 84).

Many studies have investigated the microbiology of odontogenic infections. Common to all these studies is the diversity of bacteria observed (22).

However, the literature is mixed regarding the predominant bacterial species in odontogenic infections (30, 78, 85). According to Gams et al., there are several possible explanations for this finding, including the laboratory culture technique, the protocol for transport to the laboratory and the method of sample collection (66). Previous reports show that standard culture methods of odontogenic infections yield an average of 2–8 species. When molecular techniques are used, the average is around 18 species (22, 86, 87). In addition, Walia et al. reported that the swab technique is associated with the isolation of gram-positive aerobes, whereas the aspiration technique results in more gram-negative anaerobes (30).

Furthermore, data from whole genome sequencing suggest that the role of aerobic gram-positive bacteria is overestimated when using culture-based diagnostics and that odontogenic infections are dominated by anaerobic Prevotella, Porphyromonas and Fusobacterium spp (88).

These limitations apply to our study as well. We used a swab technique followed by subsequent culture. Additionally, we had to group the results of cultures with no growth and those with a mixture of oral flora bacteria, where no further identification was conducted. This partly explains the relatively high percentage of cases (33%) in which no pathogenic bacteria were identified. Nevertheless, our findings regarding predominant bacteria are consistent with those of other authors using culture-based techniques (66, 78, 84).

Candida spp. was more frequently isolated from samples from elderly patients than from younger patients, whereas viridans group streptococci were more frequently identified in non-elderly patients. Candida spp. and viridans group streptococci are not known to be the predominant species in odontogenic infections. Therefore, the absence of viridans group streptococci, which are part of the normal oral flora, and a higher abundance of Candida spp. in the elderly may be a surrogate for an altered composition of the oral microbiome in the elderly patients included in this study. The prevalence of Candida spp. carriage has previously been shown to increase with age (89). This could be induced by previous antimicrobial therapy or denture prosthesis, which could explain the higher prevalence of Candida spp. in the elderly (90, 91).

The study has a few limitations, and some study parameters are debatable:

First, the study is a monocentric, retrospective study, all patients came from the catchment area of the Klinikum Oldenburg AöR, which represents a subpopulation in Germany.

To ensure better comparability of the study groups and to avoid possible alterations in the results, we defined a lot of stringent exclusion criteria. Nevertheless, these facts could influence the results in the sense of a selection bias and can limit the transferability of the results to other countries and ethnic groups.

Referring to the joint statement of the significant German Geriatric Societies we defined 70 years as cutoff age for elderly patients. Referring to the literature, some authors prefer 65 years as cutoff age (41, 63) again other authors use 60 years for cutoff definition (1). Nevertheless, there is no generally cutoff value for the calendared age and the resulting is a “grey area” regarding the allocation of the age group between 60 and 70 years. Despite this problem to define geriatric patients based on their calendar age, other important factors like multimorbidity, frailty and decrease of functional reserve had to be considered for the definition of the geriatric patient. An improvement for further studies could be the selection by a geriatric assessment tool.

The data from this study show, that age alone is not a risk factor for complications and longer LOS. However, in combination with specific anatomical spaces, in particular the parapharyngeal and oral base space, older patients have a higher likelihood of complications and longer LOS.

In addition, we found a significant effect of CRF on complications and LOS with an increase especially in the older population.

The present study shows that high WBC and especially high CRP levels on admission can serve as sensitive and reliable predictive markers for complications and prolonged LOS. Furthermore, in older patients, CRP is the more predictable marker of a complicated course and prolonged LOS.