Anaerobic infection is an infectious process caused by spore–forming or non-spore-forming microorganisms in conditions favorable for their vital activity. Characteristic clinical signs of anaerobic infection are the predominance of symptoms of endogenous intoxication over local manifestations, the putrefactive nature of the exudate, gas-forming processes in the wound, rapidly progressing tissue necrosis. Anaerobic infection is recognized based on the clinical picture confirmed by the results of microbiological diagnostics, gas-liquid chromatography, mass spectrometry, immunoelectrophoresis, PCR, ELISA, etc. Treatment of anaerobic infection involves radical surgical treatment of a purulent focus, intensive detoxification and antibacterial therapy.
A49.9 Bacterial infection, unspecified
Anaerobic infection is a pathological process, the causative agents of which are anaerobic bacteria that develop under conditions of anoxia (lack of oxygen) or hypoxia (low oxygen tension). Anaerobic infection is a severe form of the infectious process, accompanied by damage to vital organs and a high percentage of mortality. In clinical practice, anaerobic infection is faced by specialists in the field of surgery, traumatology, pediatrics, neurosurgery, otolaryngology, dentistry, pulmonology, gynecology and other medical fields. Anaerobic infection can occur in patients of any age. The proportion of diseases caused by anaerobic infection is not exactly known; anaerobes are sown from purulent foci in soft tissues, bones or joints in about 30% of cases; anaerobic bacteremia is confirmed in 2-5% of cases.
Anaerobes are part of the normal microflora of the skin, mucous membranes, gastrointestinal tract, organs of the genitourinary system and by their virulent properties are conditionally pathogenic. Under certain conditions, they become pathogens of endogenous anaerobic infection. Exogenous anaerobes are present in the soil and decomposing organic masses and cause a pathological process when they enter the wound from the outside. Anaerobic microorganisms are divided into:
1 Optional. They are able to survive both in the absence and in the presence of oxygen. These include E. coli, shigella, yersinia, streptococci, staphylococci, etc.
2 Obligate. Their development and reproduction is carried out in an oxygen-free environment. Obligate pathogens are divided into two groups:
- spore-forming (clostridia) – are pathogens of clostridiosis of exogenous origin (tetanus, gas gangrene, botulism, food toxicoinfections, etc.);
- non-spore-forming (non-clostridial) anaerobes (fusobacteria, bacteroids, vaillonella, propionibacteria, peptostreptococci, etc.). In most cases, they cause purulent-inflammatory processes of endogenous nature (abscesses of internal organs, peritonitis, pneumonia, phlegmons of the maxillofacial region, otitis, sepsis, etc.).
Conditions conducive to the development are damage to anatomical barriers with the penetration of anaerobes into tissues and the bloodstream, as well as a decrease in the redox potential of tissues (ischemia, bleeding, necrosis). The penetration of anaerobes into tissues can occur during surgical interventions, invasive manipulations (punctures, biopsies, tooth extraction, etc.), perforation of internal organs, open injuries, wounds, burns, animal bites, prolonged compression syndrome, criminal abortions, etc. Factors contributing to the occurrence of anaerobic infection are:
- massive contamination of wounds with earth;
- the presence of foreign bodies in the wound;
- hypovolemic and traumatic shock;
- concomitant diseases (collagenoses, diabetes mellitus, tumors);
In addition, irrational antibiotic therapy aimed at suppressing concomitant aerobic microflora is of great importance.
The main factors of pathogenicity of anaerobic microorganisms are their number in the pathological focus, the biological properties of pathogens, the presence of associated bacteria. In the pathogenesis of anaerobic infection, the leading role belongs to enzymes produced by microorganisms, endo- and exotoxins, and nonspecific metabolic factors. Thus, enzymes (heparinase, hyaluronidase, collagenase, deoxyribonuclease) are able to enhance the virulence of anaerobes, the destruction of muscle and connective tissues.
Endo- and exotoxins cause vascular endothelial damage, intravascular hemolysis and thrombosis. In addition, some clostridial toxins have nephrotropic, neurotropic, cardiotropic effects. Also, non-specific factors of anaerobic metabolism have a toxic effect on the body – indole, fatty acids, hydrogen sulfide, ammonia.
Depending on the localization, anaerobic infection is distinguished:
- central nervous system (brain abscess, meningitis, subdural empyema, etc.)
- head and neck (periodontal abscess, Ludwig’s angina, otitis media, sinusitis, neck phlegmon, etc.)
- of the respiratory tract and pleura (aspiration pneumonia, lung abscess, pleural empyema, etc.)
- of the female reproductive system (salpingitis, adnexitis, endometritis, pelvioperitonitis)
- of the abdominal cavity (abdominal abscess, peritonitis)
- skin and soft tissues (clostridial cellulitis, gas gangrene, necrotizing fasciitis, abscesses, etc.)
- bones and joints (osteomyelitis, purulent arthritis)
The course of anaerobic infection can be lightning-fast (within 1 day from the moment of surgery or injury), acute (within 3-4 days), subacute (more than 4 days).
Regardless of the type of pathogen and the localization of the infectious focus, various clinical forms have some common features. In most cases, anaerobic infection has an acute onset and is characterized by a combination of local and general symptoms. The incubation period can range from several hours to several days (on average about 3 days).
A typical sign of anaerobic infection is the predominance of symptoms of general intoxication over local inflammatory phenomena. A sharp deterioration in the general condition of the patient usually occurs even before the onset of local symptoms. The manifestation of severe endotoxicosis is a high fever with chills, pronounced weakness, nausea, headache, lethargy. Arterial hypotension, tachypnea, tachycardia, hemolytic anemia, icteric skin and sclera, acrocyanosis are characteristic.
In case of wound anaerobic infection, an early local symptom is a strong, increasing pain of a bursting nature, emphysema and crepitation of soft tissues caused by gas-forming processes in the wound. Among the permanent signs is the fetid ichorous odor of exudate associated with the release of nitrogen, hydrogen and methane during the anaerobic oxidation of the protein substrate. The exudate has a liquid consistency, serous-hemorrhagic, purulent-hemorrhagic or purulent character, heterogeneous color with inclusions of fat and the presence of gas bubbles. The putrefactive nature of the inflammation is also indicated by the appearance of the wound containing gray-green or gray-brown tissue, sometimes black scabs.
Anaerobic infection is often accompanied by the development of multiple organ failure (renal, hepatic, cardiopulmonary), infectious and toxic shock, severe sepsis, which are the cause of death.
For the timely diagnosis of anaerobic infection, the correct assessment of clinical symptoms is of great importance, allowing timely provision of the necessary medical care. Depending on the location of the infectious focus, clinicians of various specialties – general surgeons, traumatologists, neurosurgeons, gynecologists, otolaryngologists, maxillofacial and thoracic surgeons – can diagnose and treat anaerobic infection. In order to determine the pathogenic agent and the severity of the infectious process , use:
- Methods of pathogen detection. Methods of rapid diagnosis of anaerobic infection include bacterioscopy of the wound discharge with a Gram smear stain and gas-liquid chromatography. In the verification of the pathogen, the leading role belongs to bacteriological seeding of the wound or abscess contents, analysis of pleural fluid, blood seeding for aerobic and anaerobic bacteria, enzyme immunoassay, PCR.
- Other analyses. In the biochemical parameters of blood with anaerobic infection, a decrease in protein concentration, an increase in creatinine, urea, bilirubin, transaminase and alkaline phosphatase activity is detected.
- Instrumental diagnostics. Along with clinical and laboratory studies, radiography is performed, in which gas accumulation is detected in the affected tissues or cavities.
Anaerobic infection must be differentiated from erysipelas of soft tissues, polymorphic exudative erythema, deep vein thrombosis, pneumothorax, pneumoperitoneum, perforation of hollow abdominal organs.
An integrated approach to the treatment of anaerobic infection involves radical surgical treatment of a purulent focus, intensive detoxification and antibacterial therapy. The surgical stage should be performed as early as possible – the patient’s life depends on it. As a rule, it consists in a wide dissection of the lesion with the removal of necrotic tissues, decompression of surrounding tissues, open drainage with washing of cavities and wounds with antiseptic solutions. The peculiarities of the course of anaerobic infection often require repeated necrectomies, the opening of purulent pockets, the treatment of wounds with ultrasound and laser, ozone therapy, etc. With extensive tissue destruction, amputation or exarticulation of the limb may be indicated.
The most important components of the treatment of anaerobic infection are intensive infusion therapy and antibiotic therapy with broad-spectrum drugs highly resistant to anaerobes. As part of the complex treatment of anaerobic infection, hyperbaric oxygenation, UVI of blood, extracorporeal hemocorrection (hemosorption, plasmapheresis, etc.) are used. If necessary, antitoxic anti-gangrenous serum is administered to the patient.
Prognosis and prevention
The outcome of anaerobic infection largely depends on the clinical form of the pathological process, the premorbid background, the timeliness of diagnosis and the start of treatment. The mortality rate in some forms of anaerobic infection exceeds 20%. Prevention of anaerobic infection consists in timely and adequate treatment of wounds, removal of foreign bodies of soft tissues, compliance with the requirements of asepsis and antiseptics during operations. With extensive wound injuries and a high risk of anaerobic infection, specific immunization and antimicrobial prophylaxis are necessary.