The document discusses bloodstream infections, including the etiological agents, types, clinical manifestations, laboratory diagnosis, and fever of unknown origin. It defines various types of bloodstream infections such as bacteremia, septicemia, and fungemia. The document also outlines the diagnostic process for bloodstream infections including specimen collection, culture methods, identification, and antimicrobial susceptibility testing.

1. Bloodstream
Infections
Dr Neeta Khokhar
Assist. Professor
Microbiology Dept
GMERS Medical College
Gandhinagar

2. Learning objectives
At the end of the session, the students will be able to understand:
▰ Etiological Agents of BSI
▰ Types of Bloodstream Infections
▰ Clinical Manifestations and laboratory Diagnosis
▰ Fever of Unknown Origin (FUO)
2

3. INTRODUCTION
▰ Blood stream infections (BSI) - presence of microorganisms in blood -
constitute one of the most serious situations among infectious diseases.
▰ Microbial invasion of blood stream can have serious immediate
consequences such as shock, multiple organ failure, and DIC (disseminated
intravascular coagulopathies)
3

4. Terminologies
▰ Bacteremia - presence of bacteria in blood without any multiplication.
▰ Septicemia - bacteria circulate and actively multiply in the bloodstream and
may produce their products (e.g. toxins) that cause harm to the host.
▰ Presence of viruses, parasites and fungi in blood - 'viremia', 'parasitemia' and
'fungemia' respectively
4

5. Types of Bacteremia
1. Transient bacteremia:
▰ Occur spontaneously or with minor events (brushing teeth or chewing food,
instrumentation of contaminated mucosal site and surgery involving non-
sterile site)
▰ May also lead to septicemia
5

6. Types of Bacteremia (Cont..)
2. Continuous bacteremia:
▰ Organisms are released into the bloodstream at a fairly constant rate.
▰ Septic shock, endocarditis and other endovascular infections.
6

7. Types of Bacteremia (Cont..)
3. Intermittent bacteremia: bacteria are released into blood intermittently
▰ Undrained abscess (bacteria are released approximately 45 minutes before
a febrile episode).
▰ Early course of meningitis, pneumonia, pyogenic arthritis and
osteomyelitis.
7

8. ETIOLOGICAL AGENTS OF
BSI
8

9. ETIOLOGICAL AGENTS OF BSI
Pathogens of all four major groups of microbes—
▰ Bacteria
▰ Viruses
▰ Fungi
▰ Parasites
9

10. Bacterial Etiology
▰ Bacterial agents account for the majority of bloodstream infections.
▰ Common agents causing primary BSI- typhoidal salmonellae, brucellae or
spirochetes (Leptospira, Borrelia), HACEK group of pathogens, viridans
streptococci and rickettsiae (infect vascular endothelium).
10

11. Bacterial Etiology (Cont..)
▰ Primarily infect other sites and subsequently spill over to the blood stream
to cause secondary BSI:
 Gram-positive cocci: Staphylococci, beta hemolytic streptococci,
enterococci and pneumococci),
 Gram-negative cocci: meningococci
 Gram-positive bacilli : Bacillus anthracis and Listeria
11

12. Bacterial Etiology (Cont..)
▰ Gram-negative bacilli: E. coli, Klebsiella, Enterobacter, non-fermenters
(e.g. Pseudomonas, Acinetobacter, Burkholderia, Stenotrophomonas)
Haemophilus, Aeromonas, etc.
▰ Anaerobes: Bacteroides
12

13. Viral Etiology
▰ HIV & other human retroviruses–attack CD4 T lymphocytes and
macrophages.
▰ Agents of hemorrhagic fever - dengue, chikungunya, Ebola, Marburg,
Lassa, yellow fever, and other viruses – they infect endothelial cells (Yellow
fever virus)
13

14. Viral Etiology (Cont..)
▰ Epstein-Barr virus- Invades lymphocytes - causes infectious
mononucleosis and various malignancies.
▰ Cytomegalovirus- Invades monocytes, polymorphonuclear cells, and
lymphocytes - causes hepatitis and congenital infections.
14

15. Parasitic Etiology
▰ Parasites that directly infect RBCs- Plasmodium and Babesia
▰ Parasites that may be found in the blood stream before they migrate to
other tissues or organs; e.g. include tachyzoites of T.gondii, amastigote
forms of Leishmania, and trypomastigote forms of Trypanosoma.
▰ Parasites that may be present in lymphatics and come to bloodstream
transiently; e.g. microfilariae of filarial parasites.
15

16. Fungal Etiology
▰ Fungemia - occur primarily in immunocompromised patients
▰ Candida species – MC agent; (8-10% of all nosocomial BSI) C.albicans &
non-albicans Candida species - C. tropicalis, C. parapsilosis & C. auris
▰ Agents of systemic mycoses (Histoplasma, Blastomyces, Coccidioides, and
Paracoccidioides).
16

17. TYPES OF BLOODSTREAM
INFECTIONS
17

18. TYPES OF BLOODSTREAM INFECTIONS
▰ There are two major categories of bloodstream infections (BSIs):
 Intravascular
 Extravascular.
18

19. Factors contributing to initiation of BSI
▰ Immunosuppression
▰ Use of broad-spectrum antimicrobial agents
▰ Invasive procedures
▰ Extensive surgeries that allow the bacteria to access the blood
▰ Prolonged survival of debilitated patients
19

20. Intravascular Bloodstream Infections
▰ They originate within the cardiovascular system which includes:
 Infection of the heart (endocarditis, myocarditis and pericarditis)
 Infection of blood vessels
20

21. Extravascular Bloodstream Infections
▰ Organisms multiply at the primary site such as lungs and are drained by
lymphatics and reach the bloodstream.
▰ The organisms are either removed by the cells of the reticuloendothelial
system or they multiply more widely and thereby causing septicemia.
21

22. Extravascular Bloodstream Infections
(Cont..)
▰ Portal of entry:
 Most common portals of entry - genitourinary tract (25%),
 Followed by respiratory tract (20%),
 abscesses (10%), surgical site wound infections (5%), and biliary tract (5%).
 In up to 25% of cases, the portal of entry remains uncertain
22

23. Bacteria causing extravascular bloodstream
infections (BSIs) and their common sources
23
Bacteria Portal of entry/sources
E. coli and other gram-negative bacteria such
as Klebsiella, Proteus, Enterobacter, Pseudomonas
Urinary tract (most common),
Intestine (rarely)
Haemophilus influenza type b Meninges, epiglottis, lungs
Pneumococcus Meninges, lungs
Brucella Reticuloendothelial system
Salmonella Typhi Small intestine, lymph nodes and
reticuloendothelial system
Listeria Intestine, meninges
Staphylococcus aureus and coagulase negative
staphylococci
Surgical site infections

24. CLINICAL
MANIFESTATIONS
24

25. CLINICAL MANIFESTATIONS
▰ BSI - have a bacteremia stage followed by a septicemic stage.
▰ Clinical manifestations are evident only in the septicemic stage - bacteria
multiply and release their products (e.g. toxins) which travel to various
organs affecting their functions.
▰ Based on the severity and the extent of organ failure – 2 stages of BSI:
sepsis and septic shock
25

26. Definition of sepsis and the assessment of
severity and organ failure
26
Sepsis
Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host
response to infection
SOFA score
Sepsis is diagnosed by SOFA (Sepsis-related organ failureassessment) score which in
turn depends on six parameters.
1. Respiratory system—PaO2/FiO2
2. Coagulation system—Platelet count
3. Liver—Serum bilirubin
4. Cardiovascular—Mean arterial pressure (MAP)
5. Central nervous system—Glasgow coma scale score
6. Renal—Serum creatinine and urine output
Organ dysfunction can be identified as an acute change in the total SOFA score ≥2
points following the infection

27. Definition of sepsis and the assessment of
severity and organ failure (Cont..)
27
qSOFA (Quick SOFA) Criteria
Determination of SOFA score takes considerable time as it depends upon a number of laboratory
parameters. However, before the result of SOFA score is available, sepsis can promptly be identified
at the bedside with qSOFA score
 Respiratory rate ≥22/min
 Altered mentation
 Systolic blood pressure ≤100 mm Hg
Septic shock
It is a subset of sepsis in which underlying circulatory and cellular/metabolic abnormalities are
profound
Patients with septic shock can be identified with a clinical construct of sepsis with:
 Persisting hypotension requiring vasopressors to maintain MAP (mean arterial pressure) ≥65 mm
Hg and
 Serum lactate level >2 mmol/L (18 mg/dL) despite adequate volume resuscitation
Patients with septic shock have a mortality of >40% in contrast to 10%, for sepsis cases

28. LABORATORY DIAGNOSIS
28

29. Specimen Collection for Blood Culture
▰ Site: Blood for culture should always be collected in pairs; from two
separate venipuncture and 2 separate skin decontamination process.
▰ Preparation of the site: To avoid contamination with skin flora, blood
should be collected under strict aseptic conditions using sterile disposable
syringe.
▰ Skin decontamination
▰ Timing of collection: Blood - collected before starting antimicrobial 29

30. Specimen Collection for Blood Culture
(Cont..)
▰ Blood volume: At least 8–10 mL of blood per bottle for an adult and 1–3
mL per pediatric bottle is recommended.
▰ Number of blood cultures: At least 2–3 blood culture sets (each set
consists of two bottles: 1 aerobic and 1 anaerobic) are required.
▰ Dispensing: Collected blood is then directly dispensed into either blood
culture bottle at the bedside (conventional or automated blood culture).
30

31. Specimen Collection for Blood Culture
(Cont..)
▰ Transport of blood specimen: The collected blood is gently mixed with the
broth and then transported immediately to the Microbiology laboratory.
▰ In case of delay, blood culture bottle should never be refrigerated.
▰ It can be kept at 350C in an incubator (if available) or left at room
temperature.
31

32. Steps of collection of blood for culture
32

33. Conventional Culture Medium
Types of media:
▰ A. Monophasic medium:50–100 mL
of brain heart infusion (BHI) broth.
▰ B. Castaneda’s biphasic medium: BHI
agar slope and BHI broth
33

34. Conventional Culture Medium (Cont..)
▰ Dilution: The blood is inoculated in the medium at a dilution of 1:5 so that
the antibacterial components in the blood, if any, will get diluted.
▰ SPS (sodium polyanethol sulfonate) is added to the medium as an
anticoagulant. It also counteracts the bactericidal action of blood.
▰ Incubation: Upon receipt, the bottles should be directly incubated in the
upright position at 37° C for up to 7 days.
34

35. Conventional Culture Medium (Cont..)
▰ Repeat subcultures are made from the BHI broth onto blood agar and
MacConkey agar.
35

36. Automated Culture Media
▰ BACTEC and BacT/ALERT
▰ Bact/ALERT Virtuo- most advanced system
▰ Growth is continuously monitored, & reading is
recorded every 15–20 min.
36

37. Automated Culture Media (Cont..)
▰ When the growth is detected, the system gives a positive signal.
▰ Then the bottle is removed and processed similarly as done for
conventional bottles.
37

38. Identification
▰ The isolated organism is identified by colony morphology, Gram staining,
followed by either conventional biochemical reactions or automated
identification system such as MALDI -TOF or VITEK.
38

39. Antimicrobial Susceptibility Test
▰ AST is carried out for guiding the institution of appropriate therapy.
▰ MIC based method (e.g., VITEK) is preferred over disk diffusion
▰ It is ideal for endocarditis isolates, especially while reporting susceptibility
of penicillin.
39

40. Treatment
▰ Due to higher prevalence of MDROs and higher mortality in sepsis,
antibiotics should be instituted at the earliest, as soon as sepsis is clinically
suspected.
40

41. Treatment (Cont..)
▰ De-escalation approach is usually followed:
▰ Empirical treatment consists of higher class of antimicrobials with both
gram-negative and gram-positive coverage; e.g. carbapenem such as
meropenem plus vancomycin.
 Definitive treatment can be tailored according to AST report.
41

42. FEVER OF UNKNOWN
ORIGIN (FUO)
42

43. FEVER OF UNKNOWN ORIGIN (FUO)
▰ Reserved only for prolonged febrile illnesses without an established
etiology despite of intensive evaluation and diagnostic testing.
43

44. Definitions
▰ Petersdorf and Beeson had defined FUO in 1961 as patients having:
 Temperatures of >38.3°C (>101°F) at least on two occasions; duration
of more than 3 weeks
 Failure to reach a diagnosis despite 1 week of inpatient investigation
44

45. The current definition of FUO
▰ 1. Fever ≥38.3°C (≥101°F) on at least two occasions
▰ 2. Duration of illness of ≥3 weeks
▰ 3. No known immunocompromised state
▰ 4. Diagnosis that remains uncertain after a thorough history-taking,
physical examination, and the following obligatory investigations:
45

46. The current definition of FUO (Cont..)
▰ 4. Diagnosis that remains uncertain after a thorough history-taking,
physical examination, and the following obligatory investigations:
 ESR and CRP (C-reactive protein) level
 Platelet count, leukocyte count (total and differential), and
hemoglobin
 Electrolytes, creatinine, total protein, ferritin and protein
electrophoresis
 Enzymes - alkaline phosphatase, alanine aminotransferase, aspartate
aminotransferase, lactate dehydrogenase, creatine kinase 46

47. The current definition of FUO (Cont..)
 Antinuclear antibodies, and rheumatoid factor
 Urinalysis
 Culture: blood cultures (3 negative cultures) and urine culture
47

48. Etiology of FUO
▰ Infections (36%) - This accounts for majority of FUO cases.
▰ Neoplasms (19%) - lymphoma, leukemia, myeloma, renal, colon & liver Ca
▰ Non-infectious Inflammatory Diseases (19%) - connective tissue disorders
like rheumatoid arthritis, SLE etc.
▰ Miscellaneous Causes (19%) – Granulomatous diseases, inherited &
metabolic diseases etc.
▰ Undiagnosed cases (7%).
48

49. Infectious causes of fever of unknown origin
49
Bacterial causes
Localized pyogenic infections Systemic bacterial infections
 Appendicitis
 Cholangitis
 Cholecystitis
 Localized abscess
 Mesenteric lymphadenitis
 Osteomyelitis
 Pelvic inflammatory disease
 Sinusitis
 Suppurative thrombophlebitis
 Intravascular infections
 Mycobacterial infections
 Typhoid fever
 Rickettsial infections
 Melioidosis
 Listeriosis
 Bartonellosis
 Actinomycosis and Nocardiosis
 Spirochete infections:
 Syphilis
 Lyme disease
 Relapsing fever
 Leptospirosis

50. Infectious causes of fever of unknown origin (Cont..)
50
Non-bacterial causes
Viral infections Parasitic infections Fungal infections
 Cytomegalovirus and
EBV infection
 Coxsackie virus group B
infection
 Viral hepatitis
 HIV infection
 HSV infection
 Dengue
 West Nile virus infection
 Colorado tick fever
 Hantavirus infection
 Parvovirus infection
 Malaria
 Amoebiasis
 Leishmaniasis
 Chagas’ disease
 Toxoplasmosis
 Strongyloidiasis
 Echinococcosis
 Schistosomiasis
 Toxocariasis
 Aspergillosis
 Mucormycosis
 Blastomycosis
 Histoplasmosis
 Coccidioidomycosis
 Paracoccidioidomyc
osis
 Candidiasis
 Cryptococcosis
 Pneumocystis
infection
 Sporotrichosis

51. Laboratory Diagnosis- Specimen Collection
▰ Prior to specimen collection, a complete clinical history (including details
of travel, immunization, exposure to any other patients) and physical
examination should be carried out - may be helpful in choosing the
appropriate specimen
51

52. Laboratory Diagnosis - Microscopy
▰ Blood microscopy
▰ Stool wet mount
▰ Gram stain of pus, sputum and other specimens
▰ Ziehl-Neelsen stain for M. tuberculosis.
▰ PAS or GMS stain
52

53. Laboratory Diagnosis - Culture
▰ Blood culture - typhoid fever, brucellosis
▰ Culture on Lowenstein Jensen medium - M. tuberculosis
▰ Culture of pus and exudate specimen from the abscesses
▰ Sabouraud dextrose agar (SDA) culture - fungal isolation
▰ Cell line culture
53

54. Laboratory Diagnosis - Serological Tests
▰ ELISA and rapid tests for viral diseases - hepatitis B and C, HIV, CMV, EBV
infections, etc.
▰ Standard agglutination test: For brucellosis
▰ Microscopic agglutination test: For leptospirosis
▰ Cold agglutination test: For Mycoplasma
▰ Weil Felix test: For rickettsial diseases
54

55. Laboratory Diagnosis - Serological Tests
(Cont..)
▰ Paul-Bunnell test: For infectious mononucleosis
▰ Widal test: For typhoid fever
▰ Microimmunofluorescence test for chlamydial infections
▰ Rheumatoid arthritis (RA) factor: For rheumatoid arthritis
55

56. Laboratory Diagnosis - Molecular Tests
▰ PCR can be carried out to amplify the specific genes
56

57. Laboratory Diagnosis - Other Tests
▰ Complete blood count: Increased neutrophil count indicates pyogenic
infections
▰ Raised ESR (erythrocyte sedimentation rate)
▰ Histopathological examinations of the biopsies obtained from tumors
may suggest the underlying etiology
57

58. Laboratory Diagnosis - Other Tests (Cont..)
▰ Imaging methods: Chest X-ray (for diagnosis of tuberculosis) and CT or
MRI scan to identify the malignant tumors and their extension
▰ ECG and echocardiography: Rheumatic fever and IE
58

59. INFECTIONS CAUSING
ANEMIA
59

60. List of microorganisms causing anemia
60
Iron deficiency anemia
It occurs due to blood loss, which occurs as a result of infection with various agents, leading to
microcytic hypochromic anemia.
 Hookworm (Necator americanus and Ancylostoma duodenale)
 Trichuris trichiura
 Schistosoma species
Hemolytic anemia
It occurs due to destruction of RBCs. The various infectious agents include:
 Malaria (Plasmodium falciparum)
 Babesia microti
 Bartonella bacilliformis
 Clostridial sepsis (Clostridium perfringens)
 Infectious mononucleosis (Epstein-Barr virus)
 Hepatitis A virus

61. List of microorganisms causing anemia
(Cont..)
61
Megaloblastic anemia
 It is caused by a parasite, Diphyllobothrium latum
 It causes dissociation of vitamin B12- intrinsic factor complex with in the gut lumen, which leads to decreased
absorption of vitamin B12 in ileum.
Aplastic anemia
Aplastic anemia occurs as a result of bone marrow dysfunction (or failure) leading to a normocytic normochromic type of
anemia. This can occur due to infection with various agents such as:
 M.tuberculosis , Rickettsial infections
 Leishmania donovani , Cytomegalovirus (CMV)
 Epstein-Barr virus , Varicella-zoster virus
 Parvovirus B19 (aplastic crisis in patients with chronic hemolytic anemia)
 Human immunodeficiency virus (HIV) , Human herpesvirus 6 (HHV-6)
 Hepatitis C virus

62. Questions:
▰ Q1. Examples of intermittent bacteremia:
a. Brushing teeth
b. Septic shock
c. Endocarditis
d. Undrained abscess
62

63. Questions:
▰ Q2. Which of the following is a component of qSOFA score:
a. Altered mentation
b. Respiratory system—PaO2/FiO2
c. Cardiovascular—Mean arterial pressure (MAP)
d. Central nervous system—Glasgow coma scale score
63

64. Questions:
▰ Q3. Infections causing megaloblastic anemia:
a. Babesia microti
b. Diphyllobothrium latum
c. Bartonella bacilliformis
d. Leishmania donovani
64

65. THANK YOU