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Bacteremia
MLAB 2434 –Microbiology
Keri Brophy-Martinez
Definitions

Pseudobacteremia
False bacteremia
 Contamination of a blood culture
during or after collection

Definitions

Bacteremia – presence of bacteria in blood
stream


Some conditions have a period of bacteremia
as part of the disease process (ex. Meningitis,
endocarditis)
Usually occurs due to a disruption of skin or
mucosal barriers to bacterial invasion
Classifications of
Bacteremia
Classified
 Classified
 Classified
 Classified

by Site of Origin
by Causative Agent
by Place of Acquisition
by Duration
Classification by Site of Origin



Primary Bacteremia
 Blood stream or endovascular bacterial
invasion with no preceding or simultaneous
site of infection with the same
microorganism
Secondary Bacteremia
 Isolation of a microorganism from blood
as well as other site(s)
Fever of Unknown Origin (FUO)

Source unknown
Classification by Causative Agent
Gram positive bacteremia
 Gram negative bacteremia
 Anaerobic bacteremia
 Polymicrobial bacteremia

Classification by Place of Acquisition

Community-acquired

Health-care acquired/Nosocomial

Defined as occurring 72 hours post
admission
Classification by Duration

Transient



Intermittent


Comes and goes
Usually occurs after a procedural
manipulation (ex. Dental procedures)
Can occur from abscesses at some body
site that is “seeding” the blood
Continuous Bacteremia

Organisms from an intravascular source
that are consistently present in
bloodstream
Sepsis & Septicemia



Presence of active bacteria
Results from continuous bacteremia
Clinical signs and symptoms of bacterial
invasion and toxin production


Apply the SIRS criteria
Systemic response to bacterial infection
Bacteremia Complications

Septic shock
 Results from body’s reactions to bacterial
bi-products
• Endotoxins: lipopolysaccharide
• Exotoxins
 Disrupts many body functions
• Hemodynamic changes, decreased
tissue perfusion and compromised organ
& tissue function
 Mortality 40% to 50%
Bacteremia/Septicemia Risk
Factors




Immunocompromised patients
 Due to decrease in circulating neutrophils
Increased use of invasive procedures &
indwelling devices
 Disrupts normal flora
Age of patient
 Young: defect in humoral immunity
 Old: Decreased immune competency
Administration of drug therapy
 Broad spectrum antibiotics decrease
normal flora
 Increase in antimicrobial resistance
Sources of Bacteremia
Pericarditis and Peritonitis
 Pneumonias
 Pressure sores
 Prosthetic medical devices
 Total hip replacement
 Skeletal system
 Skin and soft tissue
 Urinary Tract Infections

Clinical Signs and
Symptoms





Abrupt onset of chills, fever, or
hypothermia and hypotension
Prostration (exhaustion/weakness) and
diaphoresis (perspiration)
Tachypnea (rapid breathing) is an early
sign of bacteremia
Delirium, stupor, agitation
Nausea, vomiting
Clinical Signs and
Symptoms (cont’d)

Laboratory Values in Bacteremia







Thrombocytopenia
Leukocytosis or leukopenia
Acidosis
Abnormal liver functions
Coagulopathy
DIC
Elevations in CRP, haptoglobin, fibrinogen,
ESR, procalcitonin
Specimen Collection

Positive blood cultures
Critical value
 Physician correlates finding to
clinical picture to verify septicemia


Best Practice
Collect specimen immediately PRIOR
to rise in temperature
 Collect PRIOR to antibiotic therapy

Specimen Collection

Aseptic collection procedure is critical
 Cleansing agents
• Tincture of iodine (1-2%)
•
Leave on skin for 30 seconds
• Povidine-iodine (10%)
•
Leave on skin 1.5 to 2 minutes
• Chlorhexidine/ChloraPrep
•
•
Leave on skin for 30 seconds
2% chlorhexidine gluconate + 70% isopropyl alcohol

Cleansing Technique

Acceptable Contamination Rate
• In concentric fashion, from inside to out
• After cleaning, wait 1.5-2 minutes
• 1-3%
Collection sites

Preferred
Peripheral venous
 Arterial sites


Less common
Central venous catheters
 Arterial lines

Blood Collection Devices



Traditional set
 Aerobic bottle
• Selects for aerobic & facultative
anaerobes
 Anaerobic bottle
• Selects for obligate anaerobes
ARD bottle (Antibiotic Removal Device)
 Used when patient is on antibiotics
prior to blood collection
SPS= Sodium polyanetholsulfonate
Blood Collection Devices

Anticoagulants
 SPS= Sodium polyanetholsulfonate
• Function/Purpose
• Anticoagulant
• Neutralizes human serum
• Prevents phagocytosis
• Inactivates certain antimicrobial agents

SAS(sodium amylosulfate)
• Similar to SPS, but less effective in neutralizing
serum
Specimen Collection:
Blood Volume



Ideal ratio of blood: broth
 1:5 to 1:10
 Dilution aids in preventing the bactericidal
effect of WBCs & complement
Volume Recommendations by Age
 Younger than 10 years- 1 mL of blood for
every year of life
 Over 10 years- 20 mL
Short draw?

Inoculate anaerobic bottle first
Specimen Collection:
Frequency of Collection
Depends if bacteremia is transient,
intermediate or continuous
 General guidelines



Usually x2 from different body sites,
when patient is spiking a fever
Endocarditis
• 3 sets from 3 different sites within 1-2 hours
of clinical presentation

Fever of Unknown Origin (FUO)
• Initially 2 sets; 24-36 hours later, obtain 2
more
Specimen Collection:
Frequency of Collection

If a catheter-related bloodstream infection
is suspected:


One set drawn peripherally
One set drawn via catheter
Blood Culture Methods

Conventional Broth Systems
 Aerobic broth contains soybean casein digest
broth, tryptic or trypticase soy broth, Brucella
agar or Columbia broth base
 Anaerobic broth is usually the same as aerobic
with addition of 0.5% cysteine in an aerobic
environment
 Must be subcultured and gram stained manually, at
12, 24 and 48 hours
 Method not recommended due to risk of
needlestick and contamination; not cost effective
Blood Culture Methods
(cont’d)

Biphasic Broth-Slide System
 Agar “paddles” attached to top of bottle;
includes CA, MAC, malt extract agars
 Incubate at 35 OC for 7 days
 Allows for blind subcultures
 Closed system
Blood Culture Methods
(cont’d)

Lysis-Centrifugation Blood Culture Systems (Isolator)
 Used in the recovery of Fungus and AFB
 The Isolator is a special tube that contains
saponin, a chemical that lyses cells and other
anticoagulants
 Approximately 7.5-10 ml of blood is placed in the
tube, then centrifuged to concentrate
microorganisms; sediment is subcultured to fungal
and/or mycobacterial media
Blood Culture Methods
(cont’d)

Automatic Blood
Culture Systems

BacTec 9000 Series
• Fluorescent light is used
to detect changes in
CO2 levels
Bactec 9000 Series
Automatic Blood Culture
Systems (con’t)

ESP( Extra Sensing Power)
 Now VersaTREK
 Measures
consumption/production
of gases; such as CO2 H2,
N2 and O2 in the
headspace of each bottle
 Detects a change in
pressure
Automatic Blood Culture
Systems (con’t)
• BacT-Alert
• Carbon dioxide
production results in
a pH change
• pH change results in
color change
detected by system
as “positive”
Blood Culture Workup


Incubation times

Routine aerobic/anaerobic

Endocarditis

Brucellosis/Fungemia/HACEK
• 5-7 days
• 2 weeks
• 21-28 days
Reporting results


Initial report is sent out at 24 hours
Final report is sent out at 5-7 days for all
no growth specimens
Blood Culture Workup

Positive Cultures




Gram stain the bottle to determine the
morphology of the organism present
Call the results of the gram stain to the
physician or nurse, including how many
sets etc., so that antibiotic therapy can be
initiated
Subculture to appropriate media
Identify organism and perform sensitivity
testing
Blood Cultures: Pathogens

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Staphylococcus aureus
Streptococcus pneumoniae
Haemophilus influenza
Pseudomonas species
Neisseria species
Coagulase negative Staphylococcus species
(immunocompromised)
Group B Streptococcus (infants)
Alpha hemolytic Streptococcus viridans group
Gram negative rods
Yeasts and molds
Anaerobes
Blood Cultures:
Contaminants
Coagulase negative Staphylococcus
 Propionibacterium acnes
 Alpha hemolytic Streptococcus
viridans group
 Bacillus species
 Diphtheroids
 Growth of multiple organism

Treatment & Prevention

Treatment




Empirical treatment, initially, with broad
spectrum antibiotic
Antisepsis therapy; physiological support,
anticoagulation agents, glucocorticoids
Adjunctive measures; draining fluids,
removing catheters
Prevention

Vaccines; S. pneumo, influenza, varicella
References
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Broyles, M. (2013, June). A Closer Look at Sepsis. ADVANCE for
Medical Laboratory Professionals, 25(5), 12-13.
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http://www.bd.com/ds/productCenter/212536.asp
http://www.bd.com/ds/productCenter/445718.asp
http://www.temple.edu/medicine/microbiology_lab.htm
Kiser, K. M., Payne, W. C., & Taff, T. A. (2011). Clinical Laboratory
Microbiology: A Practical Approach . Upper Saddle River, NJ:
Pearson Education.
Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of
Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.