Bacteremia, septicemia, and most common cause

Last updated on May 14th, 2021

Pathogens of all four major groups of microbes- bacteria, fungi, viruses and parasites may be found circulating in blood during the course of many diseases.

Presence of bacteria in the blood is called bacteremia. Bacteria may reach to bloodstream

  • from an existing focus of infection
  • from a site with commensal flora
  • or  by direct inoculation of contaminated material into the vascular system (i.e. trauma).

On the basis of duration of presence of bacteria in the blood, bacteremia  is classified as;

  1. Transient bacteremia,
  2. Continuous bacteremia and
  3. Intermittent bacteremia.

These bacteria are often cleared from the blood within minutes by immune cells but if the immune system is overwhelmed or evaded organisms may persist in the blood, resulting in the symptoms and signs of septicemia.  Although septicemia (literally sepsis of the blood) implies a more serious clinical condition than bacteremia (literally presence of bacteria in the blood), in practice many clinicians and microbiologists used the term interchangeably.

Difference between “Bacteremia” and “Septicemia”

Traditionally the term bacteremia referred to the transitory presence of bacteria in the blood of a patient in the absence of symptoms; the origin of bacteria was usually from a site of commensal colonization. The term septicemia meant the presence of bacteria in the blood with clinical signs and symptoms of infection. Their origin was from a focus of infection from which they entered the circulation.

The difference is largely ignored in new medical literature and publications. The presence of fungi in blood is termed as fungemia.

Lists of most common cause of bacteremia and fungemia are:

Gram negative organisms associated with bacteremia

  1. Escherichia coli  (most common cause)
  2. Klebsiella spp.
  3. Enterobacter spp.
  4. Proteus spp.
  5. Salmonella typhi
  6. Salmonella spp. other than S. typhi
  7. Pseudomonas aeruginosa
  8. Neisseria meningitidis
  9. Haemophilus influenzae
  10. Bacteroides fragilis (anaerobe)
  11. Brucella spp.
  12. Burkholderia (Pseudomonas) pseudomallei  (in certain areas)

Gram Positive organisms associated with bacteremia

  1. Staphylococcus aureus (Most common cause)
  2. Staphylococcus epidermidis
  3. α-Haemolytic (viridans) Streptococci
  4. Streptococcus pneumoniae
  5. E. faecalis (group D)
  6. S. pyogenes (group A)
  7. S. agalactiae (group B)
  8. Listeria monocytogenes
  9. Clostridium perfringens
  10. Peptostreptococcus spp. (anaerobes)


  1. Candida albicans; Cryptococcus neoformans etc.

About Acharya Tankeshwar 468 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.

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