Microbiology of hospital infections

2021-08-21 05:13 PM

Opportunistic infections are caused by bacteria in the bacteriophage of the patient and are often unavoidable because of the involvement of the mucosal barrier

Nosocomial infection is an infection that occurs during the patient's stay in the hospital, this infection is neither manifested nor in the incubation period when the patient is admitted to the hospital. Hospital-acquired infections that manifest only after the patient leaves the hospital are also included. Although many nosocomial infections are preventable, some are not preventable, so nosocomial infections are not equivalent to physician infections i.e. infections resulting from diagnostic or therapeutic interventions such as urinary catheterization. a catheter, or venous catheter. Opportunistic infections occur in patients with impaired defense mechanisms and are usually caused by infectious agents that would not normally cause disease in healthy individuals.

Microorganisms causing hospital infections

The most common are Gram-negative aerobic bacteria, staphylococci, enteric streptococci.

Gram-negative bacilli are the most important of the nosocomial infections because they are the main causative agents of urinary tract infections and cause disease in other sites. Enteric bacilli such as E. coli, Klebsiella are commonly found in nosocomial infections in patients with impaired defense mechanisms. Many Gram-negative bacilli such as Pseudomonas and Klebsiella have minimal nutritional requirements, which can create disease clusters in the hospital environment as well as inpatients. Gram-negative bacilli develop drug resistance faster than Gram-positive cocci, Gram-negative bacilli become resistant through harvesting of the R plasmid. In addition, Enterobacter, Pseudomonas, and Serratia also have chromosomal mutation mechanisms that prevent chromosomal mutations. resistant to penicillin and cephalosporins.

Among Gram-positive cocci, S. aureus is still an important pathogen. It often causes infections of surgical wounds, burns, and venous catheters. Staphylococcus aureus is found everywhere, in the skin, hair, pharynx of patients and hospital staff, in the hands of hospital staff, in tools, and in most objects found in hospitals. Many resistant strains of S. aureus are found in many hospitals, which can cause outbreaks of infection in intensive care units. They are resistant to erythromycin, clindamycin, and aminoglycosides. Methicillin-resistant staphylococcus aureus (MRSA: methicillin-resistant S. aureus ) is also a common cause of nosocomial infections in many parts of the world: in Denmark with a rate of 0.1%, in Sweden 0. 3%, Netherlands 1.5%, Switzerland 1.8%,

Enterococci have long been known to be an important nosocomial urinary tract infection agent, which is of significance in the wound healing of patients treated with cephalosporins. Many enterococci strains are resistant to aminoglycosides such as gentamicin and vancomycin

The list of microorganisms important in nosocomial infections is growing dramatically. Opportunistic infections caused by virulent bacteria (S. epidermidis) and fungi (Aspergillus, Candida) are also common. Clostridium difficile colitis is the result of a change in intestinal flora caused by antibiotic treatment.

Respiratory viruses such as respiratory syncytial virus and influenza virus, and recently SARS (severe acute respiratory syndrome) coronavirus are nosocomial infectious agents. Other viruses such as hepatitis virus and HIV are associated with infections caused by transfusions of blood or blood products, or by stroke. Cytomegalovirus, varicella-zoster virus, and rotavirus also play a significant role in nosocomial infections, which cause nosocomial infections in immunocompromised individuals, in patients with axillary muscle transplantation.

Disease reservoir

Healthcare workers, patients, and visitors are the primary reservoirs.

Most hospital-acquired infections come from bacteria that live on the patient's body

Pathogenic bacteria usually reside in the following locations: nasal cavity such as staphylococcus aureus, methicillin-resistant staphylococcus; on the skin S. epidermidis; in the gastrointestinal tract such as enterococci, intestinal bacteria, Candida species. In the genitourinary tract enterococci, are bacteria of the intestinal family.

Patients with infections or in a state of carriers of resistant bacteria such as drug-resistant enterococci, methicillin-resistant staphylococcus, Clostridium difficile will contaminate the environment. And the contaminated environment becomes a secondary reservoir. Some environments are the first reservoirs of some pathogenic bacteria such as water containing Legionella bacteria, Pseudomonas species; food containing digestive tract bacteria

Microbial transmission in hospital-acquired infections

Direct transmission

In hospitals, healthcare workers' hands are often temporarily contaminated and often act as vectors

for the transmission of bacteria from one person to another. Healthy healthcare workers often carry pathogenic bacteria such as Staphylococcus aureus, Streptococcus pyogenes, and Salmonella enteritidis and transmit these bacteria to sick people.

Transmission by instrument

Instruments such as electronic thermometers, medications, intravenous fluids, food, milk, and oral solutions can transmit bacteria that cause hospital-acquired infections to patients.

Spread through the air

Hospital air, ventilation systems can transmit agents such as M. tuberculosis, varicella-zoster virus, SARS coronavirus, Aspergillus species of fungi. Contaminated water dust can transmit Legionella bacteria

Factors affecting hospital-acquired infections

As with most infections, UTI is the result of an interaction between two factors 

Microbial factors

Virulence and spread of pathogenic microorganisms,

The patient's resistance

Age, disease, mucosal and skin integrity, and immune status are major determinants of morbidity and outcome of nosocomial infections. Mechanisms of defense: physical (attenuated in case of burns or trauma), chemical (lack of hydrochloric acid, gastrectomy that limits gastric acidity) or immunological (Hodgkin's disease, chemotherapy) anti-cancer, etc.) strongly affects nosocomial infections.

In addition to the patient and microbiology, other factors associated with nosocomial infections include diagnostic and functional measures, therapeutic modalities, and patients at high risk for nosocomial infections. immunocompromised patients, patients treated with drugs that reduce protection (corticosteroids, etc.), and patients during treatment are subject to multiple interventions. Increased use of trauma diagnostic methods increases the probability of nosocomial infections.

Hospital staff is also at risk of nosocomial infection, staff in laboratories with blood samples can contract viral hepatitis, HIV and infectious diseases (tuberculosis, pertussis...).