Bacteremia

MLAB 2434 –Microbiology Keri Brophy-Martinez

Definitions Pseudobacteremia

False bacteremiaContamination 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 by Site of Origin Classified by Causative Agent Classified by Place of Acquisition Classified 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/NosocomialDefined as occurring 72 hours

post admission

Classification by Duration Transient

Comes and goes Usually occurs after a procedural

manipulation (ex. Dental procedures) Intermittent

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

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 Complications

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 valuePhysician correlates finding to clinical

picture to verify septicemia

Best PracticeCollect specimen immediately PRIOR

to rise in temperatureCollect 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• In concentric fashion, from inside to out• After cleaning, wait 1.5-2 minutes

Acceptable Contamination Rate• 1-3%

Collection sites Preferred

Peripheral venousArterial sites

Less commonCentral venous cathetersArterial 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• 5-7 days

Endocarditis• 2 weeks

Brucellosis/Fungemia/HACEK• 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

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 Broyles, M. (2013, June). A Closer Look at Sepsis. ADVANCE for

Medical Laboratory Professionals, 25(5), 12-13. http://www.achats-publics.fr/Fournisseurs/BIOMERIEUX.htm htt

p://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.