2. Objectives
• At the end of the session, the students will be able to understand:
– Define bacteremia and differentiate this condition from septicemia
– Classify each type of bacteremia and describe when each condition
occurs.
– Discuss the epidemiology and pathogenesis of bacteremia.
– Associate specific organisms with each type of bacteremia
– Explain the pathophysiology of sepsis and septic shock
– Describe the proper procedure for blood culture collection.
– Discuss the methods for the detection of bacteremia,
– Describe therapies for sepsis and septic shock.
3. Outline of lesson
• Introduction
• Epidemiology
• Microbiology
• Pathogenesis
• Clinical manifestation
• Laboratory diagnosis and AMST
• Treatment and prevention
5. 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)
6. Bacteremia vs. septicemia
• 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.
7. What is septicemia and Sepsis?
• Sepsis is defined as life-threatening organ dysfunction
caused by a deregulated host response to infection.
– Evidence of organ dysfunction includes clinical and laboratory
abnormalities of the respiratory system, coagulation, liver,
cardiovascular system, nervous system, and kidneys
8. Types of Bacteremia
• Classification by Duration
– 3 type (transient, intermittent ,Continuous. Fig 1)
9. 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)
• Usually small number of microbes and cleared by the
immune
• But May also lead to septicemia or sepsis
10. Type of …….
2,.Intermittent bacteremia
– Organisms from Undrained abscess (bacteria are released
approximately 45 minutes before a febrile episode).
– Or due to Early course of meningitis, pneumonia, pyogenic arthritis and
osteomyelitis.
– organisms are periodically released from the primary site of
infection into the blood
11. Type of …….
3. Continuous bacteremia:
– Organisms from an intravascular source released
into the bloodstream at a fairly constant rate.
– present in the bloodstream
– Septic shock, endocarditis and other endovascular
infections.
12.
13.
14. • Classification by Place of Acquisition
– Community-acquired bacteremia,
• occurs in individuals living in the general community
– Nosocomial or health care associated
• bacteremia occurs in patients who are hospitalized or
living in a nursing home or other facility.
• occurring more than 48 -72 hours after hospital
admission
• more likely to be due to resistant organisms that express
β-lactamases
15. • Classification by site of origin
– There are two major categories of bloodstream infections (BSIs):
Primary bacteremia or Intravascular
occurs when the bacteria are present in an endovascular source such as an
infected cardiac valve
Infection of the heart (endocarditis, myocarditis and pericarditis)
or an infected intravenous catheter,
secondary bacteremia
Organisms comes from an infected extravascular source, such as the
lung in patients with pneumonia.
Refer Cardiovascular diseases
16. • Extravascular
– 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.
19. 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).
26. Viral
• LEARNING OBJECTIVE
– Describe the epidemiologies of Burkitt's
lymphoma, infectious mononucleosis. and CMV
inclusion disease
– Compare and contrast the causative agents,
vectors. reservoirs, and symptoms of yellow fever.
dengue. dengue hemorrhagic fever. and
chikungunya fever,
– Compare and contrast the causative agents,
reservoirs. And symptoms of Ebola hemorrhagic
fever and Hamavirus pulmonarysyndrome.
27. 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)
• Epstein-Barr virus- Invades lymphocytes - causes infectious mononucleosis and
various malignancies.
• Cytomegalovirus- Invades monocytes, polymorphonuclear cells, and lymphocytes -
causes hepatitis and congenital infections.
• Hemorrhagic Fevers
• Chikungunya Fever
28. 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).
33. Signs and Symptoms
• Sepsis and septic shock: 2 stages of Septicemia
• Septicemia is characterized by fever (over 38°C, 99°F),
chills, nausea, vomiting, diarrhea, shortness of breath,
malaise (feeling of general discomfort), and changes in
mental status such as confusion, anxiety, and an impending
feeling of doom.
• These signs and symptoms can progress rapidly to septic
shock, a condition of extremely low blood pressure
resulting from dilation of blood vessels. Decrease in body
temperature, decrease in or absence of urine output, rapid
breathing, aberrant blood clotting, increased heart rate,
anxiety, and death characterize septic
36. Clinical DX: Sepsis
SOFA score
• Sepsis is diagnosed by SOFA (Sepsis-related organ failure assessment) score which in
turn depends on six parameters. (Laboratory 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
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
37. • Septic shock
• 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
38.
39. Who is at Risk to Develop Sepsis?
• Host Factors
– Elderly account for 60-85 percent of all cases of severe
sepsis
• Immunosuppression
– Disease related, medications related
• Exposure risk
– Community acquired: pneumonia, urinary, wounds,
trauma
– Health care acquired: invasive devices, secondary
infections and skin breakdown
41. LAB DX
• 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
therapy
42. • 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).
43. • 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
44.
45. • 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.
• Repeat subcultures are made from the BHI broth onto blood agar
and MacConkey agar.
46. • Other specimens
• Culture of IV catheter tips
• Wound Swabs
• Burn Swab
• Urine: UTI
• Sputum: RT infections
• Stool: GIT infections
47. Automated system
• BACTEC and BacT/ALERT
• Bact/ALERT Virtuo- most advanced system
• Growth is continuously monitored, & reading is recorded
every 15–20 min
• When the growth is detected, the system gives a positive
signal.
• Then the bottle is removed and processed similarly as done
for conventional bottles.
48. 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
49. Non culture techniquies
• Direct Microscopy: eg. Borrelia spp.
• LAT: GB strptococci, H. influenza type b, S.
pneumoniae, N. meningitiidis, Staph.
50. AMST
• AMST 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.
51. 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
• Empirical treatment consists of higher class of antimicrobials with both
gram-negative and gram-positive coverage; e.g. carbapenem such as
meropenem plus vancomycin.
• Combination therapy in the case of polymicrobial infections
Definitive treatment can be tailored according to AMST report.
Intravenous fluid to prevent shock
52. Brucellosis
Obligate aerobic, fastidious, small gram-
negative coccobacallus.
Brucellosis (undulant fever) - primarily a zoonotic
disease affecting various domestic animals, such
as sheep, goat or cattle
Human infection - associated with occupational
or domestic exposure to infected animals or their
products.
53. Nomen species: Important nomen species
associated with human infections are as follows:
B. melitensis -pathogenic to sheep, goat
and camel; man is also a susceptible host
B. abortus - acquired from cattle and buffalo
B. suis - infects most often pigs
B. canis – causes abortion in dogs.
54. Structure of Ag
▰ Two major types of lipopolysaccharide (LPS) antigens - M &
A
▰ Present in varying proportion in three major species of
Brucella:
B. melitensis - M antigen is predominant
B. abortus - A antigen is predominant
B. suis - either M or A antigens
55. ▰ Sources of infection:
Infected animals excreting the organisms in urine, milk,
placenta or vaginal discharge
Contaminated animal food products – dairy products,
especially soft cheeses, milk, icecream and rarely raw
meats and bone marrows
▰ Occupational risk - farmers, shepherds, goatherds,
butchers and abattoir workers in endemic areas.
56. Transmission: From infected animals to man by various modes
Direct contact- direct contact of abraded skin or mucosa with
the infected animal tissue, blood, urine, vaginal discharge or
placenta
Food-borne - unpasteurized milk or dairy products or
undercooked meat
Air-borne - inhalation of dust or aerosols in the infected
cowshed or slaughterhouses
Person-to-person- breast milk or tissue transplantation or
blood transfusions.
57. Pathogenesis
▰ Spread: From the initial site of infection, the organisms spread to
bloodstream resulting in bacteremia and then disseminate to involve
various organs.
▰ Organs involved: Reticuloendothelial system, such as lymph nodes,
spleen, liver and bone marrow. Other organs such as placenta,
musculoskeletal tissues and genitourinary systems are also involved.
▰ Local tissue response: Initially, neutrophilic infiltration occurs - later on
replaced by chronic inflammatory cells leading to granuloma formation.
▰ Intracellular survival: The cell-wall LPS appears to be the major
virulence factor - plays a key role in their intracellular survival.
58. ▰ Classic triad: Profuse night sweats, arthralgia/ arthritis and
hepatosplenomegaly . Foul-smelling perspiration is considered as a
classical sign, but uncommon.
▰ Typhoid-like illness (except that it is less acute, less severe with undulating
pattern of fever and more musculoskeletal symptoms)
▰ Undulating fever - typical remittent course, i.e. in between febrile periods
(which last for weeks), there will be afebrile periods (Malta fever or
Mediterranean fever)
▰ Musculoskeletal symptoms (Vertebral osteomyelitis or Septic arthritis)
▰ Other nonspecific symptoms - abdominal pain, headache, diarrhea, etc.
▰ CNS, CVS and Genitourinary manifestations
59. Lab dx
▰ A. Blood culture bottles (Biphasic medium);
▰ B. Automated
▰ C. Gram-stained smear of Brucella species
showing small gram-negative coccobacilli
60. Specimens: Blood, bone marrow, etc.
Blood culture by:
Castaneda’s biphasic media (BHI broth/agar)
Automated techniques such as BACTEC
Culture smear and motility testing: Reveals non-
motile, gram-negative coccobacilli
Biosafety precautions: highly infectious pathogen, all laboratory procedures should be carried out
with adequate biosafety precautions
61. ▰ Serological tests (antibody detection)
Standard agglutination test (SAT)- detects IgM
Tests to detect IgG antibody -2ME test, ELISA
62. ▰ Standard regimen in adults: Gentamicin for 7 days plus
doxycycline for 6 weeks. Streptomycin can be given
alternative to gentamicin
▰ WHO regimen in adults: Rifampin for 6 weeks plus
doxycycline for 6 weeks
▰ Relapse or treatment failure occurs in 5–10% of cases
▰ For CNS involvement: Ceftriaxone - added to the regimen
and treatment - prolonged for 3–6 months.
63. ▰ General precautions such as:
▰ Use of pasteurized milk or properly cooked food
▰ Use of protective measures to prevent direct contact with
animals.
▰ Vaccine: Live attenuated B. abortus 19–BA - available for
human - provides short term protection and had shown high
reactogenicity.
64. Borrelia
▰ Larger spirochete, 10–30 μm in length; consists of
lesser number (3–10) of spirals.
▰ Most of the species of Borrelia occur as commensals
on the buccal and genital mucosa.
▰ Few are pathogenic to men, such as:
B. recurrentis causes epidemic relapsing fever
B. burgdorferi is the agent of Lyme disease
B. vincentii causes an ulcerative
gingivostomatitis called
▰ Vincent’s angina, in association with fusiform bacilli
65. ▰ Characterized by recurrent episodes of fever and
nonspecific symptoms following exposure to insect vector
carrying Borrelia species.
▰ Relapsing fever is of two types:
1. Epidemic RF - Caused by B. recurrentis and
transmitted by louse.
2. Endemic RF - caused by Borrelia species other than
B. recurrentis such as B. duttonii, B. hermsii andB.
turicatae. It is transmitted by tick.
66. ▰ Mode of transmission - Relapsing fever is vector-borne.
▰ Epidemic RF - Transmitted by human body louse (Pediculus
humanus).
Borreliae are introduced by crushing of the louse (e.g. by
scratching) - deposition of numerous spirochetes on the
abraded skin and mucous membranes
▰ Endemic RF - Transmitted by bite of an infected tick
(Ornithodoros species).
67. ▰ From the inoculated site, Borrelia spreads rapidly - bacteremia and
fever.
▰ Host’s immune system tries to eliminate the bacilli from the body.
▰ Borrelial surface antigens frequently undergo antigenic variation.
▰ Each time, new antigens are produced - evade host’s immune
system leading to repeated bacteremia and recurrent febrile
episodes.
68. ▰ Incubation period is about 7–8 days.
▰ Recurrent febrile episodes lasting for 3–5 days occur
intervening with afebrile periods of 4–14 days.
▰ Hemorrhages: Petechiae, epistaxis and blood-tinged
sputum - epidemic RF
▰ Neurologic features - meningitis, seizure, focal deficits,
paraplegia and psychosis
69. Lab dx
▰ Microscopy:
Peripheral thick or thin smear-stained by Wright- or Giemsa-stain
Direct fluorescent antibody test using monoclonal antibody (species
identification)
Dark ground or phase-contrast microscopy - demonstrate motile
spirochetes (but low sensitivity)
It is poorly gram-negative.
▰ Culture:
During afebrile period, microscopy fails to detect Borrelia -
confirmation is made by isolation of Borrelia from blood
▰ Serology - Done for detection of antibodies.
ELISA and IFA (indirect fluorescence assay)
70.
71. ▰ Antibiotics - doxycycline or erythromycin - drug of choice for
relapsing fever.
▰ Recommended schedule is single dose for epidemic RF, and
7–10 days course for endemic RF.
72. Lyme disease or Lyme borreliosis
▰ Borrelia burgdorferi-
▰ Widespread in USA
▰ Rodents and deer are main reservoirs
▰ Transmitted by tick bite
73.
74. ▰ Stage 1: Early localized infection (annular maculopapular lesion
at the site of the tick bite - erythema migrans)
▰ Stage 2: Early disseminated infection (hematogenous spread -
secondary annular skin lesions, arthralgia, malaise and
neurological abnormalities)
▰ Stage 3: Late persistent infection (Lyme arthritis) - arthritis of
large joints, lasting for months; which may be refractory to the
treatment.
75. ▰ Isolation of B. burgdorferi - culturing specimens like skin
lesions, blood or CSF in special medium - BSK medium
(Barbour-Stoenner-Kelly)
▰ Serology (antibody detection) - Most common method of
diagnosis of Lyme disease
▰ Molecular methods: PCR detecting specific DNA- sensitive
in joint fluid.
76. ▰ For all stages of Lyme disease - except CNS and CVS
infection:
Oral doxycycline - drug of choice,
Except for children - amoxicillin is given.
Duration of treatment - 14 days (for skin lesions) and 30-
60 days (for arthritis)
▰ For CNS or CVS infection: Ceftriaxone -14–28 days.
77. Rickettsia
• Objective
– Compare and contrast the causative agents,
vectors. reservoirs, symptoms,treatments and
preventive measures
• for plague,Lyme disease. and Rocky Mountain spotted
fever
– Identify the vector. etiology. and symptoms of five
diseases transmitted by ticks
– Describe the epidemiology of epidemic typhus.
endemic murine typhus. and spotted fevers.
78. Gram-negative bacilli obligate intracellular parasites
All associated with an arthropod vector
Pathogenic species parasitize endothelial cells
almost exclusively
Distinct groups:
• Typhus group
• Spotted fever group
• Scrub typhus group
Rickettsia species
79.
80. Pathogenesis
• The organisms enter the body
• The first step virulence is adherence to a host cell
• phospholipase A2
• Disseminate through bloodstream
– > endothelial cells by induced phagocytosis
=>> escape from phagosome =>> multiply
intracellularly =>> destroy host cell.
81. Rickettsial Diseases
• Most symptoms associated with acute rickettsial infections are nonspecific
and require further tests to make an accurate diagnosis.
• many rickettsial diseases cause mild or moderate illness
• Epidemic Typhus and Rocky Mountain Spotted Fever can be severe and may
be fatal in 20%–60% of untreated cases.
Epidemic typhus
Transmitted from human to human by body louse (Pediculus humanus) (R.
prowazekii). Incubation period: 5-15 days
• Macular rash: 4-7 days after illness and begin to fade after 1-2 days
• In severe: rash may last longer and become haemorrhagic
Recrudescent typhus (Brill’s disease) is a relapse of louse-borne typhus
appearing 10 to 40 years after the primary attack. Factors triggering the
relapse are unknown.
This typhus type is usually milder than the primary infection and is less often
fatal, presumably because of partial immunity.
82. Flea-borne fevers (Murine typhus)
• Caused by R. typhi
• Rats and their infected fleas
• Tropical and subtropical coastal regions
• Ports with large number of rats
• Disease: similar to epidemic typhus but milder
Tick-borne spotted fever (group)
• Eg: R. rickettsii, R. africae
• Can be life-threatening
• Maintained in enzootic cycle (ticks and their wild animal
hosts)
83. Scrub typhus
• Orientia tsutsugamushi (previously R.
tsutsuga..)
• Larval stages (chiggers) of mites
(Leptotrombidium)
• Hosts: Rats or other small mammals
• Scrub typhus is endemic in Asian pacific
region.
84. Laboratory Diagnosis
Serological Methods
Detection of hetrophile Abs
Weil-Felix test (Agglutination test)
Detection of Abs to Rickettsial species by:
Immunofluorescence
Latex agglutination
Enzyme immuno-assay
Death may occur before detectable levels of Ab are
present
PCR test on skin biopsy or whole blood
85. Lab Dx
Weil -Felix
• By virtue of its simplicity, it has been one of the
most widely employed tests in the “world”.
• The basis of the test is the presence of antigenic
cross-reactivity between Rickettsia spp. and certain
serotypes of Proteus spp.
• The somatic (O) antigen that cross-reacted with
anti-rickettsial antibodies
86. – Typhus group rickettsiae (e.g R. prowazeki , R.
typhi) react with P. vulgaris OX19, and
– Scrub typhus reacts with P. mirabilis OXK.
– The spotted fever group rickettsiae (: R.
rickettsii, R. africae, etc.) react with P. vulgaris
OX2 and OX19, to varying degrees, depending
on the species.
W-F
87. • W-F test suffers from poor sensitivity and
specificity (with a recent study showing:
sensitivity of ≈33% & specificity of 46%).
• In resource-limited settings, it still
remains an important tool in the
diagnosis and identification of public
health concerns, such as outbreaks of
epidemic typhus.
W-F
89. Preventive measures
• Minimize exposure to infectious arthropods and animal
reservoirs (: dogs and cats) when traveling in endemic areas.
• People should avoid handling wild animals: rats.
• No vaccines or drugs are available for preventing rickettsial
infections. But for R. prowazekii, a killed vaccine is
recommended for people at high-risk .
• Improving the quality of life of both people and wild animals.
• Pesticides are useful for rats and fleas, proper use of insect
repellents,.
• Self-examination after visits to vector-infested areas, and
wearing protective clothing are ways to reduce risk.
