INTERNSHIP DIARIES EPISODE 05 – Who Resides In Your Blood? (Blood Cultures)

It was a bright day. You reached the ICU ward and introduced yourself to the resident there.You got ready with cap and mask and asked to take vitals of patient.

"He developed a spiking fever, and the central venous catheter was removed on day 14 of treatment. Fever is not responding to antibiotics, Sir." said one resident to the  consultant.

"Send the blood for culture and inform me." said the consultant.

"Dr. Kesh , Can you arrange the items for sampling and fill up the laboratory forms?" the senior resident looks at you.

"Yes, Sir." Says you excited to know and expand your knowledge about blood culture.

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5.1 BLOOD CULTURES:

INDICATION FOR BLOOD CULTURE:

1.Where the possibility of septicemia or bacteremia is suggested by the presence of fever,shock or other signs and symptoms occurring in association with a known or suspected local infection such as sepsis in a surgical wound ,Osteomyelitis,peritonitis,Arthritis,Enteric fever.

2.Pyrexia of unknown origin (temperatures of >38.3°C (>101°F) on several occasions with fever of >3 weeks and failure to reach a diagnosis despite 1 week of inpatient investigation)

3.Unexplained leucocytosis or leucopenia

4.Suspected fungemia specially in Immunocompromised patients, HIV patients.

STEPS:

I)Obtain consent

II)Hand washing

III)Arranging items for sampling (MATERIALS REQUIRED)

·        70% isopropyl alcohol swabs

·         10% Povidone iodine swabs

·        dry cotton

·        Sterile gloves of suitable size

·        2 syringes (adult: 20 cc, paediatric: 5 cc)

·        2 needles (adult: 22 gauge or preferably larger butterfly or standard needle; paediatric: 25- or 23-gauge butterfly or standard needle)

·        Blood culture bottle (Aerobic and anerobic)

IV) vein selection

• Arterial vs venous blood

 • Indwelling arterial or venous lines

• Central or peripheral

V)Hand washing and Gloving

VI)Preparation of a skin

VII)Venepuncture and drawing a blood sample

VIII)Inoculating in blood culture bottle and shake the bottle

IX)Labelling, storing and documenting

• Ask the patient about allergies to iodine.

• Apply the tourniquet, select the site.

(Be careful that the ends of the tourniquet do not fall onto the puncture site, thereby contaminating it, if the tourniquet does accidentally touch the prepared puncture site, the site must be recleaned)

• Apply alcohol/acetone pad at the puncture site for 30 seconds till it dry.

• Apply the iodine swab, apply to puncture site, move the iodine in concentric circles outward. Keep it for 60 seconds (till it dry).

• Again, clean the site with alcohol/acetone and allow it to dry.

• Perform the venepuncture, following routine venepuncture procedures. Do not repalpate the site.

• If the blood culture is one of a series of samples to be drawn from a patient, the blood culture must be collected first.

• Withdraw needle from vein and insert into the top of the blood culture container.

(Other than syringe and needle, by closed system, consisting of vacuum bottle and double needle collection tube can be done.)

• Do not change the needle.

• Do not hold the container in your hand, this may result in a needle exposure.

• Do not push the blood. Mix the content. (An adequate space above broth ensures that blood is not injected under undue pressure and some air is still available for strict aerobes)

• Keep at room temperature.

• Label the blood specimen collected, following standard labelling procedures. Be sure to include the site used and the number of the specimen in the series ordered.

Blood Cultures should NOT be taken from the following sites

•       Veins which are immediately proximal to an existing peripheral IV cannula.

•       A femoral vein due to difficulty in skin disinfection of the site. This area poses a high risk of contamination.

•       Catheter drawn blood cultures are equally likely to be truly positive (associated with sepsis), but more likely to be colonized.

(One drawn through catheter and other drawn through vein PPV of 96%)

VOLUME OF BLOOD drawn is the single most important factor influencing sensitivity

• For adult: minimum 10 ml

 • For infant and children: 1-5 ml

1-2 ml= neonate

 2-3ml= 1 month - 2year age

 3-5ml= Older children

 • 20 ml of blood obtain in sequence is more effective and sensitive (98%) specially in intermittent bacteremia.

 • Patients who have received antibiotics should give 3 separate collections of blood. Also, one or two of which on 2nd day also.

TIMING OF BLOOD CULTURE

• Before starting antimicrobial therapy

• At the time of fever peak

 • Minimum 30-60 minute interval between 2 samples except in critically ill septic patient.

 • In continous bacteremia-timing of blood culture is not important, but in intermittent bacteremia 2 or 3 culture should be spaced an hour apart.

TEST PERFORMED AFTER SAMPLE REACH TO LABORATORY

Blood to broth ratio: 1:5 only, should not be <1:5 or > 1:10

• Agitation during incubation

-  Length of incubation: • Not more than 7 days • 5 days is sufficient • >5 day-contaminants • 7 days is useful for: • Fungemia • Bacteremia due to fastidious organisms like HACEK group, brucella, legionella • For patients suspected of endocarditis who has been treated with antimicrobial before obtaining blood culture • Mycobacterial culture > 4 weeks

• Atmosphere of incubation: aerobic and anaerobic

ASK YOUR MICROBIOLOGICAL DEPARTMENT TO HELP YOU IN SELECTION OF BROTH :

• Glucose broth: useful in endocarditis

• Bile broth: In enteric fever

• Trypticase soy broth (inhibits Neisseria and S.pneumoniae)

• Brain heart infusion broth: multipurpose broth

• Thioglycolate broth: for anaerobes

• Columbia or brucella broth

• Mycobacteria: Middlebrook 7H9 with 0.05% SPS, BHI with 0.5 % polysorbate 80

• Fungus broth

Additives in broth: • Anticoagulant- bacteria are trapped in blood clot • Antimicrobial- if patient is already in antibiotics • Anticomplementry agents- to inactivates complement action • Antiphagocytic

 Type of blood culture bottle (AEROBIC AND ANAEROBIC CULTURE BOTTLE)

• Standard aerobic bottles- most common bacterial pathogens, including aerobes, facultative anaerobes and for candidemia

• Smaller bottles are used for neonates and young children

• After inoculation, bottles are incubated aerobically.

SIGNS OF BACTERIAL GROWTH:

• Macroscopically:

-Generalized turbidity

-Hemolysis

- Gas production

- Discreate colonies on the surface of the sedimented red cells

-recoverable bacterial growth may occur before turbidity is evident.

Subculture from bottles as a routine

  • For subculture:

- Subcuture should be done at least once during the first day after 5-6 hours and at interval thereafter which should be at least twice during first 2-3 days.

• Gram stain:  Should be made and examined at the subculture stage. Any positive finding should be reported at once to clinician as the morphological type of organism may guide the physician to start antibiotic.

• Quantitative counts of bacteria in blood: Inoculate 1 ml amounts of blood into several tubes of melted agar and make pore plates either directly from patients. Another method is treat the patient sample with lytic agent. Then lysed sample is centrifuged and harvested organism cultured directly on a suitable solid medium to allow identification and to give a semi-quantitative indication of its presence in blood. (When monitoring colonization associated with a prosthesis or catheter) 

INTERPRETATION OF POSITIVE BLOOD CULTURE REPORT:

1. Whether true or contaminant (ASEPSIS, ASSES RISK FACTOR PRESENT IN PATIENT)

2.FIND THE SOURCE

3.DETERMINE THE NEED FOR TREATMENT (whether patient is toxic and in shock)

4.ADDRESS UNDERLYING INFECTIOUS FOCUS

5.LOOK FOR PATHOGEN SPECIFIC FACTORS DURING ANTIBIOTIC TREATMENT (Toxins that are produced)
6.HELPS IN IDENTIFYING OTHER RISK FACTOR WITH INFECTION (The identification of S.bovis organism also prompted the ultimate identification of colonic carcinoma, which is an underlying risk factor for S. bovis bacteremia)
7.LOOK FOR REASON OF IMMUNOCOMPROMISED STATE (Rule out malignancy or HIV as bactremia may be a result of oppurtunistic infection)

Therefore,clinical examination is of utmost important. As positive blood culture is not a disease in itself. It may be a result of underlying disease or part of complication.

After starting treatment, document the blood culture clearance duration.

SOME DEFINITIONS:

Bacteremia – presence of bacteria in blood stream.Some conditions have a period of bacteremia as part of the disease process (ex. Meningitis, endocarditis)

Septicemia – bacteremia plus clinical signs and symptoms of bacterial invasion and toxin production

Transient bacteremia lasts for minutes or a few hours and most frequently occurs after manipulation of nonsterile body sites—for example, during dental procedures; after gastrointestinal biopsy; after percutaneous catheterization of the vascular system, bladder, or common bile duct; and after surgical debridement or drainage—that is, after procedures involving contaminated or colonized skin and/or mucosal surfaces are performed and also at the onset of acute bacterial infections.

Intermittent bacteremia is defined as bacteremia due to the same microorganism that is detected intermittently in the same patient because of a cycle of clearance and recurrence. Intermittent bacteremia is often associated with undrained closed-space infections, such as intra-abdominal or soft-tissue abscesses, and may also occur in patients with liver abscesses, cholangitis, and focal infections, including pneumonia, osteomyelitis, and spondylodiscitis. 

Persistent bacteremia is a characteristic of infective endocarditis (IE) and other intravascular infections, such as vascular-graft infection, a mycotic aneurysm, or an infected thrombus. Persistent bacteremia also occurs during the early stages of systemic bacterial infections, such as brucellosis and typhoid fever.

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After labelling the sample, storing and documentation, you went to ICU again. Taking vitals and documenting it in files. Feeling happy to learn about blood culture. 

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HAPPY STUDYING !

UPASANA Y. AND JAY