Orofacial infections are infections arising from the oral cavity and face. They are either odontogenic or non-odontogenic in origin, with the vast majority being bacterial in nature. Orofacial infections are of particular concern because severe infections are prone to spread locally and regionally through fascial spaces of the head and neck, and haematogenous spread leading to systemic infection. Untreated severe orofacial infections have high morbidity and mortality. Rapid diagnosis, patient assessment and institution of definitive treatment are therefore important in ensuring positive treatment outcomes.

Neutrophils form part of the innate immune system and are the most abundant granulocytes accounting for 50% - 70% of all white blood cells. They are phagocytic and are the hall mark of acute inflammation, being among the first responders to the site of inflammation through chemotaxis, especially in bacterial infection [1][2]. Neutrophil to lymphocyte ratio (NLR) is used in clinical practice to evaluate systemic inflammation. It is elevated in certain conditions and has been found to be a valuable predictor of outcomes in a variety of diseases including cardiovascular disease, pulmonary arterial hypertension, schizophrenia, and hearing loss [3][4].

Whereas C-Reactive protein (CRP), erythrocyte sedimentation rate (ESR), and procalcitonin have been used routinely as inflammatory markers and prognostic indicators, NLR has not gained popularity in clinical practice, more so in orofacial infections. NLR is calculated from the absolute values of neutrophils and lymphocytes obtained from full blood count by dividing neutrophil count by lymphocyte count. This eliminates the need for additional test requests as would be necessary for CRP, ESR or procalcitonin levels. The ratio has been used to prognosticate mortality, progression to severe disease, increased odds and duration of intubation, risk of severe disease in intubated patients, and the need for intensive care [5].

The NLR ratio has been used to predict mortality, with specificity and sensitivity comparable to that of CRP and ESR in conditions such as pneumonia, cancer and sepsis [6]. In the head and neck region, NLR has been successfully used in the management of malignancies to demonstrate the association between chemoradiation therapy and the development of grade three mucositis [7][8]. Increased NLR has also been associated with increased length of hospital stay and duration of antimicrobial treatment in infections. Conversely, it has been shown to decrease to values approaching those of normal persons after successful treatment for infection [9][10].

This was a cross-sectional study on NLR as a predictor of outcomes in patients with orofacial infections at the Kenyatta National Teaching and Referral Hospital (KNH) in Nairobi, Kenya. Patients with a diagnosis of orofacial infections and a pre-treatment full blood count available were recruited between November 2023 and July 2024. Information on participant demographics, diagnosis, prior antibiotic use, and comorbidities was recorded. Pretreatment values of absolute neutrophil, lymphocyte counts, as well as CRP were recorded. NLR was calculated by dividing the absolute neutrophil count by the absolute lymphocyte count. The cut off for NLR was set at 2, with values above this being considered abnormal. The outcome of the treatment in terms of hospital stay, admission to the ICU or mortality was recorded at the time of discharge.

The data were analysed with R version 4.1.2. Normality was assessed using the Shapiro-Wilk test. Continuous data were described using mean and standard deviation, and median and interquartile range. Categorical data were summarised using frequencies and proportions. The Kruskal-Wallis test was used to establish any significant difference in NLR among the various outcomes. Spearman rank order correlation was used to establish the relationship between NLR values with the recorded length of hospital stay. Mortality was expressed both as an absolute count and as a proportion by dividing the number of deaths by the sample size. Logistic regression was used to assess whether NLR was associated with the outcomes. A p-value of less than 0.05 was considered statistically significant.

Out of 135 patients with orofacial infections 80 met the inclusion criteria and were recruited into the study. Of the 80 participants, 17 (21.2%) were under 5 years of age, 13.7% (11) were aged 6 - 17 years, 32.5% (26) were aged 18 - 35years, 21 (26.3%) were 36 - 60 years, and 5 (6.3%) were more than 60 years old. Most of the participants were male (71.2%, n = 57) (Table 1).

Table 1. Sociodemographic characteristics.

The finding that male participants were the most affected by orofacial infections is in agreement with two studies but contradicts another study that showed no gender predilection [11]-[13]. The observation of a significant proportion of young adults with orofacial infection has been reported elsewhere [11]. Literature posits that men are generally more prone to neglecting their oral health, maintaining poorer oral hygiene, facing higher rates of periodontal disease, and sustaining dental injuries. In contrast, women typically have more positive attitudes towards dental visits, possess greater oral health literacy, and engage in better oral health practices [14]. Mortalities higher in male participants, agrees with Omeje et al., 2016 where 73.1% of the mortalities were men [11]. The foregoing observation fits well in the explanations given by behavioural models on health-seeking behaviour between males and females, where females have better health-seeking behaviour and practices, thus seek intervention early and prevent progression of disease in early stages. The findings that the most common comorbidities associated with orofacial infections were diabetes mellitus, HIV, and hypertension match those of Shweta et al. [15].

The findings on the WBC, neutrophils, and CRP are consistent with existing knowledge that they tend to increase during an infection [16]. Length of hospital stay among participants with orofacial infections was significantly associated with increase in NLR. In agreement with the current study, a systematic review of NLR in patients with odontogenic infections revealed that an increase in the ratio was significantly associated with longer duration of hospital stay in addition to more severe disease and the need for higher doses of antibiotics after surgery [17][18]. These findings are supported by others who have reported a significant association in length of hospital stay among patients with higher levels of NLR [9][19][20]. During bacterial infections, the body’s inflammatory response is marked by an increase in neutrophils and a relative decrease in lymphocytes. This shift in balance between inflammatory cells is reflected in the NLR, a reliable indicator for diagnosing bacterial infections. The more severe the infection, the longer the hospital stay, and the higher the values will be in the laboratory tests [21]. This study showed that admission to the intensive care unit (ICU) was associated with higher levels of NLR. There was a statistically significant difference in NLR in the disease outcomes (ICU admission, mortality), indicating a strong association. The finding that the lowest NLR levels were associated with disease resolution is corroborated by other authors, as is the finding that higher NLR indicates more severe disease [21]. Higher levels of NLR have been associated with more severe disease, which can then explain the increase in mortality with higher levels of NLR [14][18].

The current study did not reveal a significant association between mortality and NLR, probably due to a smaller sample size compared to other studies [14][18], although this study showed that participants with normal NLR had lower odds of mortality compared to those with abnormal NLR, in line with findings elsewhere that NLR can significantly predict mortality among patients with odontogenic infections [18]. The lack of significance in the current study could be due to a low sample size.

The current study revealed a significant difference in NLR between participants who died and those with resolved disease among participants with orofacial infections. Similarly, CRP was also significantly different between participants who died or were admitted to the ICU and those with resolved disease. Participants with normal NLR of 2 had significantly higher odds of disease resolution compared to those with abnormal NLR. It can therefore be deduced that NLR is as good as CRP in predicting outcomes in orofacial infections, which is the standard of care in our setup. In fact, this study has shown that NLR is an independent predictor of disease resolution in orofacial infections.

NLR had a significant association with mortality and disease severity and was comparable to CRP in ability to predict disease outcomes in orofacial infections. Participants with resolved disease had significantly lower levels of NLR compared to those who were admitted to the ICU. Similarly, participants who died or were admitted to the ICU had significantly higher levels of CRP compared to those with resolved disease. NLR can be an easily accessible and good predictor of disease outcomes.

The study protocol had ethical approval from the University of Nairobi/Kenyatta National Hospital Ethics and Research Committee (No. P591/07/2023). Permission to conduct the study was obtained from the management of Kenyatta National Hospital. Informed consent was obtained from the participants at admission and where the participant was a minor, consent was obtained from the parent or the guardian.