Anaerobic oropharyngeal infections are rare, and the most frequent pathogen involved is Fusobacterium necrophorum, leading to Vincent’s angina or acute necrotizing ulcerative gingivitis [6] and, to a lesser extent, F. nucleatum and other Fusobacteria. In young patients, Vincent’s angina is responsible for Lemierre’s syndrome, a known locoregional complication of upper airway infections caused by thrombophlebitis of the jugular vein. In addition, Fusobacterium sp. are responsible for 1% of bacteremia of all origins, while 44% of bacteremia are related to anaerobic bacteria [7]. The most common species are F. nucleatum (60–70% of cases) and F. necrophorum (25–30%). F. nucleatum is less common in anaerobic oropharyngeal infections, but it must not be overlooked in the ED because it is frequently complicated by bacteremia [4].

Low-symptomatic pharyngeal forms of F. nucleatum infections, contrary to typical ENT clinical presentations of Vincent’s angina much better known by ED practitioners [6], can complicate and delay the diagnostic process. This particular presentation can lead to delayed diagnosis and increased risk of systemic complications and extraoral metastatic infections (brain, liver, joints, heart). The mortality rate associated with Fusobacterium sp. bacteremia varies from 5% to 47% [8]. In the majority of cases, bacteremia occurs in older individuals, and immunodeficiency is one of the risk factors that must be investigated [7].

The literature on the management in the ED of these ENT infections with a risk of bacteremia is rare. Numerous studies have focused on the high prevalence of F. nucleatum in colorectal cancer and its potential severity in digestive disease [9].

The present clinical case highlights the following: first, the need to be aware of major complications in cases of ENT infection without identified tonsillar infection, and second, the need to consider the possibility that these are not linked to classical aerobic bacteria as viral agents. Consequently, we should question our use of diagnostic methods for oropharyngeal infection and our antibiotic prescription decision in the ED: oropharyngeal infection associated with F. nucleatum requires a different antibiotic treatment [4] to that associated with group A streptococcus, the most frequent bacterial etiology (20%) [2] targeted by current management algorithms [1]. Fusobacterium species are naturally resistant to macrolides, quinolones, aminoglycosides, and trimethoprim molecules. Moreover, for F. nucleatum, resistance to penicillin through the production of penicillinases is increasing (30% in Europe) [10]. According to the prevalence of microbiological profiles in the general population, the common error is probably to consider a common oropharyngeal infection with a negative rapid diagnostic test for beta-hemolytic group streptococcus as a viral infection. The diagnostic process must follow an approach such as in urinary tract infections, considering negative rapid strip test. This is even more relevant in the current context, in which infection with COVID-19 is mainly sought when faced with an acute undifferentiated fever. Even though ENT manifestations in COVID-19 are less common than fever and cough, they can reach 44% in some studies [11]. The clinical reasoning must systematically integrate the search for a bacterial infection and, in particular, carry out a blood culture when considered necessary.

This clinical case shows that low-symptomatic forms of ENT infection with alteration of general condition should be considered by analogy with febrile illness entity [12], an important issue in emergency medicine: the final diagnosis of bacterial infection may not be complete, while systemic repercussions are kinetically at the forefront with a delayed initial diagnosis.

In this clinical case, a first step was facilitated by elevated serum biomarkers of inflammation, regularly implicated in severe bacterial infection [13], and initial 36-hour hospital monitoring was decided. Clinical presentation could have led to the conclusion of a severe form of “common seasonal virosis” with transient poor hemodynamic tolerance, indicating hypovolemia by dehydration. However, biological elements associating hyperleukocytosis, elevated CRP, and PCT levels, alerted us to the possibility of a systemic bacterial infection. The use of biomarkers remains an aid in the initial phase of management (Figure 6), but does not always allow conclusions of bacterial origin.

Fig. 6
figure6

Complete management from presentation to discharge: treatments, outcomes

In a second step, decreased levels of inflammatory biomarkers, associated with pyrexia, led to hospital discharge without indication for probabilistic antibiotic coverage [14]. Few studies on CRP kinetics are available to guide intrahospital management of bacterial [15] or viral infections, especially in the ED. An elevated CRP level despite antibiotic therapy is known to be useful to suspect a fluid collection, but its decrease has been poorly studied [14]. Thus, it is difficult to evaluate the relevance of the initial phase of management without antibiotic coverage.

Finally, it was the complete bacteriological diagnosis of F. nucleatum bacteremia in a third and last step that allowed a targeted etiological treatment, after a delay of 3 days, linked to a long incubation period of the Fusobacterium genus (72–96 hours of anaerobic culture).

Fortunately, a first-reasoned probabilistic treatment was administered as soon as a Gram-negative anaerobic pathogen was identified on blood culture, 24 hours before the final diagnosis, and 48 hours after the ED presentation. Moreover, carrying out blood culture is an approach with a low impact on organizational constraints and a positive medicoeconomic balance, regarding the objective of preventing septic shock.

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