Postoperative mediastinitis is a deep infection of the sternum which extends beyond the subcutaneous layer. This is one of the most feared complications in cardiac surgery.
Despite improved means of therapeutic treatment, morbidity and mortality remains high with a mortality rate ranging from 11 to 20% [3, 4].
The contamination of the surgical site is often derived from the commensal flora of the human body (patient or health care team) [5].
The most frequently identified organisms are Staphylococcus aureus (40–60%) followed by Gram-negative bacilli (BGN) (19% Enterobacteriaceae (Escherichia coli, Proteus species, Klebsiella pneumoniae) and 5 to 10% Pseudomonas aeruginosa) and anaerobes. Polymicrobial mediastinitis involving staphylococci, BGN can be seen in 4–30% of cases. Haemophilus influenzae mediastinitis cases are rare. The association between Haemophilus influenzae and Aggregatibacter aphrophilus in mediastinitis is exceptional [1, 2, 6].
In a wide range of mediastinitis in a 8-years study carried out in France (Charbonneau et al.) 3 cases of Haemophilus influenzae were found; that being a percentage of 0.9% [7].
In ower knowledge, no associations of Haemophilus influenzae with Aggregatibacter aphrophilus was found.
Haemophilus is a fastidious and polymorphic Gram-negative Coccobacilli, which usually causes a mild infection on many levels, but may also be responsible for serious infections if it reaches parts of the body where it is unusual to find it.
H.aphrophilus, also part of Haemophilus species, was recently transferred (2006) in a new genus: Aggregatibacter [8].
Commensal of the oral cavity and upper respiratory tract in children and adults, the two bacteria have been involved in various infections: endocarditis, brain abscess, meningitis, osteomyelitis and arthritis. Mediastinitis remains however a very rare location [9].
The identification of these microorganisms is based on biochemical properties but molecular biology remains more efficient (RNA 16 s or sequencing) [8].
Factors contributing to the development of post-surgical mediastinitis are multiple and dependent on the type of surgery: covers of sternotomy; postoperative bleeding and those dependent on patient history including chronic obstructive pulmonary disease, smoking, diabetes and obesity [1, 2, 5, 6, 8, 10].
In our case, the patient was smoker and diabetic and, he showed an immediate postoperative bronchitis which would likely cause the bacteremia in these two germs.
A study in Nantes on post cardiac surgery mediastinitis, shows the association of this clinical entity with pneumonia in 77% of cases, responsible for a prolongation of mechanical ventilation and, therefore an extension of stay in intensive care. This raises the question of whether the infection was transmitted to the lung by bacterial translocation or bacteremia or conversely if mediastinitis could be secondary to pneumonia [6].
Treatment of mediastinitis includes: the treatment of septic shock and associated visceral failures, antibiotic therapy and aspiration guided by ultrasound or surgical exploration with drainage [2, 5, 11].
As recommended empiric antibiotic therapy should include vancomycin or a cephalosporin, associated with an aminoglycoside or a fluoroquinolone with adjustment to the results of susceptibility testing for a period of 3 weeks [1].
The beta-lactams are top choice antibiotics for treating infections with H.influenzae both in adults and in children. However, there are many mechanisms of resistance, the most common being the production of beta-lactamase. It is primarily TEM-type enzyme. A decreased susceptibility to beta-lactams by modification of the penicillin binding proteins (PBPs) target this antibiotic family is another mechanism which can add an efflux mechanism [7, 8, 10, 12, 13].
The in vitro activity of various antibiotics tested showed that cefotaxime and cefpodoxime have better activity in terms of MIC 50 and MIC interval, followed by amoxicillin + clavulanic acid that restores the activity of amoxicillin over the stem producing only beta-lactamase. Cefuroxime and cefaclor are less active in vitro regardless of the phenotype of the strains tested. Similar results have been reported in Europe and North America [7, 8, 10, 12, 13]. The Poor dissemination of beta-lactams and glycopeptides bone level often leads to associate with other molecules, such as fluoroquinolones, rifampin or fucidin [14].
For our patient, antibiotic therapy was at first probabilistic based on vancomycin associated with fluoroquinolone then was switched to aminopenicillin following the result of MICs with fluoroquinolone for a period of 3 weeks.
