Septicemia and Systemic Inflammatory Response Syndrome (SIRS)

Bacteria entering the blood is called bacteremia. If the bacteria are not killed or removed by body defenses but rather multiply in the blood they can cause septicemia. Septicemia occurs when microorganisms get into the blood and cause harm to the body. This is considered a medical emergency since it can frequently lead to systemic inflammatory response syndrome (SIRS), also known as septic shock (def).

Epidemiology

The most common cause of mortality in the intensive care unit is septic shock . Even with the best treatment mortality ranges from 15% in patients with sepsis to 40-60% in patients with septic shock.

Septic shock develops in about 40% of sepsis patients. Death due to septic shock increased 82.6% from 1979 to 1997 in the US, with approximately 4.2 deaths per 100,000 population. Around 750,000 cases of sepsis are diagnosed per year and around 31% of those diagnosed die. The annual health care cost from caring for patients with sepsis is $5-10 billion.

A number of factors contribute to the increasing incidence of sepsis:

• Widespread us of corticosteroid (def) and immunosuppressive therapies for organ transplants and inflammatory diseases.
• Aggressive cancer chemotherapy and radiation therapy.
• Longer lives of patients predisposed to sepsis, the elderly, diabetics, cancer patients, patients with major organ failure, and with granulocytopenia (def).
• Increased use of invasive devices such as surgical protheses, inhalation equipment, and intravenous catheters (def) and urinary catheters (def).
• Neonates (def) are more likely to develop sepsis.
• Indiscriminate use of antimicrobial drugs that create conditions of overgrowth, colonization, and subsequent infection by aggressive, antimicrobial-resistant organisms.
  

Organisms

Although septic shock can be caused by viruses and fungi, most is due to bacterial infections.

Common Gram-negative bacteria causing septic shock include opportunistic normal flora of the intestines such as Escherichia coli, Klebsiella species, Enterobacter species, and Proteus species. Another opportunistic gram-negative causing septic shock is Pseudomonas aeruginosa. The most common obligate anaerobe to cause sepsis is Bacteroides fragilis. Approximately 45% of the cases of septicemia are due to gram-negative bacteria.

Common Gram-positive bacteria causing septic shock include Staphylococcus aureus, Streptococcus pneumoniae, and Enterococcus species that are normal flora of the intestines. The most common cause of neonatal sepsis is Group B Streptococcus (GBS). Approximately 45% of the cases of septicemia are due to gram-positive bacteria.

Approximately 10% of the cases of septicemia are due to fungi, mainly the yeast Candida.

The sources for sepsis are infections elsewhere in the body. Certain organisms are frequently associated with certain source sites:

• lung infections: Streptococcus pneumoniae, Haemophilus influenzae, Legionella species, Chlamydia pneumoniae.
• wound, soft tissue infections: Streptococcus pyogenes, Staphylococcus aureus, Clostridium species, Pseudomonas aeruginosa, anaerobes, coagulase-negative Staphylococcus species.
• urinary tract infections: Escherichia coli, Klebsiella species, Enterobacter species, Proteus species, Enterococcus species.
• central nervous system: Streptococcus pneumoniae, Neisseria meningitidis, Listeria monocytogenes, Escherichia coli, Haemophilus influenzae, Pseudomonas aeruginosa, Klebsiella species, Staphylococcus species.

Symptoms

Symptoms of sepsis are usually nonspecific and include fever, chills, and constitutional symptoms of fatigue, malaise (def), anxiety, or confusion. These symptoms are not limited to infection and may be seen in a variety of noninfectious inflammatory conditions.

According to guidelines established by the American College of Chest Physicians: Society of Critical Care Medicine Consensus Conference. Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis. Crit. Care Med. 20:864-875, 1992**, a patient is diagnosed with Systemic Inflammatory Response Syndrome (SIRS) when the patient presents with two or more of the following criteria:

1. temperature > 38°C or < 36°C
2. heart rate > 90 beats/minute
3. respiration > 20/min or PaCO₂ < 32mm Hg
4. leukocyte count > 12,000/mm³, < 4,000/mm³ or > 10% immature (band) cells.

Sepsis was defined as the systemic host response to infection with SIRS plus a documented infection. Severe sepsis was defined as sepsis plus end-organ dysfunction or hypoperfusion. Septic shock was defined as sepsis with hypotension, despite fluid resuscitation, and evidence of inadequate tissue perfusion.

While SIRS, sepsis, and septic shock commonly are associated with bacterial infection, bacteremia may not be present. Bacteremia is the presence of viable bacterial within the liquid component of blood. Bacteremia may be transient, as it commonly is after injury to a mucosal surface. Bacteremia may be primary (without an identifiable focus of infection) or, more often, secondary (with an intravascular or extravascular focus of infection).

The mortality rate in SIRS has been reported to be about 7%, that in sepsis is about 16-20%, and that in septic shock is about 45%.*

** as reported in eMedicine Online: Septic Shock, by J Stephan Stapczynski, MD, Chair, Associate Professor, Department of Emergency Medicine, University of Kentucky Chandler Medical Center

For a much more detailed descriptions of sepsis, see eMedicine Online: Septic Shock.