Microbiology- a clinical approach by Anthony
Strelkauskas et al. 2010
Chapter 25: Infections of the blood
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Blood has access to the entire body.
Infections in the blood easily become
systemic and systemic infections can have
devastating effects on the patient.
Up to this day sepsis has high mortality rate.
Blood infections require aggressive
treatment.
ANATOMY OF THE CARDIOVASCULAR SYSTEM
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Depending on type of organism blood infections
are classified as:
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Bacteremia
Viremia
Fungemia
Parasitemia
Can lead to sepsis and septic shock
◦ The latter in particular with gram negative bacteria
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Intravascular infections when pathogens enter blood
and damage the structures of cardiovascular system
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Endocarditis – infection of heart
Thrombophlebitis – infection in veins
Endoarteritis – infection of arteries
Catheter associated infections
Extravascular infections
◦ Original infection is in a tissue outside of the circulation
◦ Pathogens get access to the lymphatics and eventually the
blood and disseminate into other tissues
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Infection of heart
valves
Once referred to as
bacterial endocarditis
◦ Now known organisms
other than bacteria can
cause it
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Infection involves
several factors:
◦ Alteration of the
endothelium
◦ Inflammatory response
caused by circulating
pathogens
◦ Transient bacteremia
◦ Immune complexes
rheumatic fever
cardiac attack
lung emboli
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Infectious endocarditis classified in two
ways:
◦ Acute – high fever and toxicity
 Can result in death within few days or weeks
◦ Subacute – low fever, weight loss, and night sweats
 Death can take weeks to months
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Antibiotic therapy must be aggressive
◦ Include bacteriocidal drugs given in high
concentration but aren’t toxic
◦ Balancing act that can be difficult
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Course of therapy can be prolonged
◦ More than four weeks
Dental procedures are dangerous for people
predisposed to infectious endocarditis
◦ Need to take high doses of antibiotics before dental
procedures and for 6-12 hours after
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Large numbers antibiotic-resistant bacteria in hospitals
Implantation of intravenous lines potentially serious
Infection from intravenous line or catheter, blood
colonized by organisms normally found on skin.
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In a healthy host, quickly dealt with by host defense.
In debilitated hosts, bacteremia can persist.
Increase chances of infectious endocarditis, distal infections
Commonly S. epidermis, S.aureus, Cornyebacterium species
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Intravenous fluid can also become contaminated
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Removal and treatment with antibiotics will normally
remedy catheter bacteremia.
◦ Commonly Gram-negative rods such as Pseudomonas
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Most common sources of bacteremia:
◦ Urinary tract infections
◦ Respiratory infections
◦ Skin infections
Gram negative bacteria cause much more
severe disease due to endotoxin (LPS;
lipopolysaccharide) of cell wall
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Septicemia
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Sepsis
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Severe sepsis
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Septic shock
◦ Presence of bacteria in blood with severe symptoms
◦ Bacteria present (and proliferating) in blood and
dissemination into various with organ dysfunction
◦ Induces a systemic inflammatory response
syndrome
◦ Fever, chills, and tachycardia
◦ Reduced urine, systemic acidosis, and changes in
mental status
◦ Sepsis + decreased blood pressure
◦ Sepsis + low blood pressure cannot be controlled
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Early diagnosis is critical
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Also requires:
◦ Resolution depends on more than treatment with
antibiotics
◦ Adequate maintenance of tissue perfusion
◦ Careful fluid electrolyte management
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Plague:
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Brucellosis:
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Lyme disease
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Rickettsia disease:
◦ Reservoir are rats, transmitted
by fleas and from human to
human; hemorrhagic necrosis,
septic shock
◦ Zoonosis from farm animals,
undulant fever and granuloma
◦ Reservoir are mice , transmitted
by ticks
◦ Chronic disease: skin, joint and
CNS are affected
◦ Reservoir are rodents,
transmitted by fleas or lice
◦ Obligate intracellular
◦ Infect the endothelial cells
leading to hemorrhages
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Yellow fever
◦ Liver cells are primary
target
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Dengue fever
◦ 4 serotypes
◦ Infection with a second
serotype can lead to severe
manifestation
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Ebola virus
◦ Kill vascular cells, patient
bleeds to death
◦ High mortality rate,
◦ 60 – 80% within few days
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There are several important and
dangerous parasitic infections of the
blood:
◦ Plasmodium - malaria
 Protozoa
 Asia, Africa
◦ Trypanosoma - Chaga’s disease
 Latin America
 Protozoa
◦ Filaria –elephantiasis
 Africa, Latin America, Pacific Islands, Asia
 roundworm
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Because blood and lymph travel to all parts of the
body, they are good ways to spread infection.
The presence of bacteria in the blood is referred to
as bacteremia, viruses in the blood as viremia, fungi in
the blood as fungemia, and parasites in the blood as
parasitemia.
Intravascular infections arise from pathogens gaining
entrance to the blood; extravascular infections occur
when tissue infections overflow into the blood.
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Bacterial infections of the blood include plague,
brucellosis, and Lyme disease, and rickettsial
infections like Rocky Mountain spotted fever, and
epidemic or endemic typhus.
Viruses that cause infection of the blood include
dengue fever virus, yellow fever virus, and Ebola
virus.
The three most important parasitic infections of the
blood are malaria, toxoplasmosis, and schistosomiasis,
but Chagas’ disease and filariasis are also common
parasitic infections of the blood.
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10:45am – 1:15pm
Lecture, Chapter End Self Study Questions
100 Multiple Choice Questions: 2 points each x
100 = 200 points
~65%: Chapters 14-26
~35%: Chapters 1-13
Please bring Scantron and No. 2 pencil
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Chapter 22 Infections of the Digestive System
1. The most common source of gastrointestinal
infection in the developed world is
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A. Salmonella
B. Shigella
C. Escherichia
D. Campylobacter
E. Staphylococcus aureus
Correct answer is D. Campylobacter