DNIs are potentially fatal and require an aggressive diagnostic and therapeutic management. In the pre-antibiotic era, pharyngeal/tonsillar infection were responsible for 70% of deep neck space infection [10,11]. Usually, DNIs occur after previous uncontrolled infections such as tonsillitis, dental infections, surgery, head and neck trauma or lymphadenitis after upper airways infection [12, 13], while, it is sometimes difficult to find the origin of DNI because the primary source of infection may precede it by weeks [7].
The management of DNIs involve surgical or needle drainage of the abscess associated with the use of intravenous antibiotics [14,15,16]. DNIs require timely treatment with IV antibiotics at the time of diagnosis because of the rapidly progressive nature of these infections. Antibiotic therapy should be empirically initiated, based on local epidemiology, ideally before culture and sensitivity results are available [1]. Until now, various empiric antibiotics for deep neck infection have been proposed (17,18, 19]. This fact highlights the importance of epidemiological studies in DNIs microbiology, since these studies help to determine the proper empirical treatment in each geographical area. In Greece, to our knowledge, this is the first study focused on the etiology of DNIs.
The DNI microbiology is characterized by generally being polymicrobial including aerobic and anaerobic bacteria. Among the agents commonly found are bacteria that are part of the pharyngeal flora such as S. pyogenes S. aureus, Streptococcus group C, Streptococcus anginosus, Fusobacterium sp., Prevotella sp., and Klebsiella pneumoniae. Previous studies have demonstrated that S. pyogenes, S. aureus, Streptococcus viridans and Haemophilus influenza are the most common bacterial species [20,21]. However, Adovica et al have found that the most frequently pathogens in bacterial cultures were Gram-negative rods such as Acinetobacter baumannii, Enterobacter cloacae, Pseudomonas aeruginosa and K. pneumoniae [22].
In our series, cultures have obtained from 462 out of 610 patients, while 255 of them were positive for one microorganism at least. The most common bacteria isolated were S. pyogenes and S. aureus in adults and in children as well. Most studies report a lower prevalence of DNI in children compared to adults [3,23,24]. Probably this may be caused by the history of antibiotics abuse, especially in colds and other viral infections, which are more prevalent in children than in adults [25,26]. In our study children comprised 5,6% of total patients. According to the literature, the effect of age on the distribution of most common bacteria causing DNI is not clear. Age was a significant factor influencing bacteriology of DNI in a study by Coticchia et al [27]. On the other hand, other authors did not find any significant differences in bacteriology of DNI between various age groups. In our study, the incidence of anaerobic bacteria was higher in adults compared to children. However, we have not noticed any significant correlation between bacteriology and age.
Finally, interesting finding was that 16S rRNA PCR followed by sequencing analysis detected bacterial DNA in thirty-three specimens that gave culture-negative results; nineteen of them were found to be positive for anaerobic bacteria such as A. israellii and F. necrophorum. Since none of these patients had taken antimicrobial therapy before admission, the failure of the conventional cultures to isolate these microorganisms could be related to the inappropriate sample collection combined with the fragility of the bacteria and the short incubation time of the anaerobic culture. In addition, 16S rRNA PCR identified correctly the causative microorganisms which were isolated from 150 samples, while, the results obtained by the molecular methods were available sooner than that obtained from cultures (mean time two versus five days). However, this molecular assay failed to detect bacterial DNA in 105 culture-positive samples, probably due to the low microbial load. It is known that the sensitivity of the 16S rRNA PCR, when it is applied directly to the clinical samples, is depending on the bacterial concentration. On the other hand, the culture of the low-microbial load clinical samples combined with an elongation of the time of incubation time enhances the growth of microorganisms, giving more positive results than the molecular method. Unfortunately, this molecular approach, which uses the 16S rRNA PCR combined with Sanger analysis, is not able to identify more than one microorganism per sample. Probably in the future, the implementation of the next generation sequencing technology could solve this limitation.