Introduction to Infectious Disease

Question 1

What are some mechanical lines of defence against pathogens?

Answer 1

Physical barriers (ex. skin)

Chemical barriers (stomach acid)

Mucus and cilia protect our respiratory tract

Urine flushes out bacteria from our urinary tract

Other bacteria are present on our skin and within our digestive system

Question 2

What cells are in the innate immune system and what are their roles?

Answer 2

Innate Immune System:
Macrophages and monocytes (antigen-presenting cells and surveillance)
Neutrophils (defense against bacteria and fungus)
Eosinophils (defense against parasites and response to allergies)
Basophils (respond to allergies)

Question 3

What cells are in the adaptive immune system?

Answer 3

T- and B-lymphocytes. These cells are very specific in their targeting and are able to remember pathogens via memory cells.

The adaptive immune system can also be broken into two parts:
Humoral mediated (within the serum)
Cellular mediated (within the cells)

Question 4

Describe T-lymphocytes in further detail

Answer 4

T-lymphocytes are activated by an antigen-presenting cell (macrophages and monocytes)

Activated T-lymphocytes recruit other dormant T-lymphocytes

Activated T-lymphocytes are differentiated into the following groups:

Helper cells/CD4+ (secrete interleukins and interferons. Helper cells also stimulate CD8+ cells and production of antibodies

Cytotoxic cells/CD8+ (kill cells recognized as foreign)

Regulating cells (regulates the T-lymphocyte response)

Question 5

Describe B-lymphocytes in further detail

Answer 5

B-lymphocytes are activated once an antigen is detected, often with help from T-lymphocytes

Activated B-lymphocytes are differentiated into two groups:

Plasma cells (secrete antibodies)

Memory cells (important in future attacks)

Antibodies bind to antigens, effectively trapping the antigen or clumping them together

Question 6

What is an infection?

Answer 6

A response of host immune systems and person gets ill
ex. pneumonia

Question 7

What is a sub-clinical infection?

Answer 7

A specific response in the body is evoked (antibody production), but person is not ill. The host does not become ill because the immune system is able to fight off the pathogens early

Question 8

What is colonization in terms of pathogens in the body?

Answer 8

Presence of organism at a body site without production of disease
ex. skin wounds colonized with staph

Question 9

How do pathogens cause disease?

Answer 9

Simple invasion of the microorganism can trigger immune responses. These immune responses can be perceived as illness

Some pathogens may elaborate toxins that can directly damage cells (it almost become more important to deal with the toxins before the pathogens themselves)
ex. Botulinum toxin, tetanus, staph aureus food poisoning

Question 10

What bacteria are found in typical skin microbiota?

Answer 10

Diphtheroids (ex. Corynebacterium sp.)
Propionibacteria (P. acnes)
Staphylococci (especially coagulase-negative strains)
Streptococci

Question 11

What bacteria are found in typical GI tract microbiota?

Answer 11

Bacteroides sp.
Clostridium sp.
Diphtheroids
Enterobacteriaceae (ex. E. coli, Klebsiella sp.)
Fusobacterium sp.
Streptococci (anaerobic)

Question 12

What bacteria are found in typical upper respiratory tract microbiota?

Answer 12

Bacteroides sp.
Haemophilus sp.
Neisseria sp.
Streptococci

Question 13

What bacteria are found in typical genital tract microbiota?

Answer 13

Corynebacterium sp.
Enterobacteriaceae sp.
Lactobacillus sp.
Mycoplasma sp.
Staphylococci
Streptococci

Question 14

Is the host defence (innate and adaptive immune system) important in curing infections?

Answer 14

Yes, it is the most critical aspect of curing an infection

Question 15

Are antibiotics always effective in treating susceptible infections?

Answer 15

No, especially if the immune system is not operating normally

For better efficacy, the following procedures can be used:

Drainage of abcess

Removal of dead tissue (dead tissue has no blood supply; therefore antibiotics cannot reach these tissues)

Removal of foreign bodies or prosthetic devices (infections develop on these objects and will often develop biofilms)

Decrease in immune impression therapy (ex. transplant patients have to ease off on immunosuppression drugs in order to fight off an infection, risking organ transplant rejection)

Question 16

What factors weaken host defense?

Answer 16

Malnutrition
Extremes of age
Immune globulin deficiencies
Deficiencies in cellular immunity
Alcoholism
Diabetes
Immunosuppressive therapy (anticancer drugs, corticosteroids, transplant drugs)
Invasive procedures

Question 17

What are some clinical manifestations of infection?

Answer 17

1. non-specific symptoms (malaise, loss of appetite, headaches, myalgia, arthralgias)
2. Fever (due to infection unless proven otherwise)
3. White Blood Cell counts (Normal range is 5-10 10^9 cells/L, but anything over 1010^9 cells/L could be an infection)
4. Other non-specific manifestations (anemia, increased ESR and C-reactive protein (CRP) values in blood work, increased procalcitonin, increased heart rate, anxiety, and confusion)
5. Septic Shock (decreased BP, CO, and blood O2, decreased renal and hepatic function)

Question 18

How are infections diagnosed?

Answer 18

1. History (signs and symptoms, source of infection, likely pathogen)
2. Physical Examination (will be different for each infection, but the goal is to localize the infection) ex. neck stiffness in meningitis
3. Laboratory (WBC and differential, ESR and CRP, renal and hepatic function, electrolytes, microbiology(gram stain, culture and sensitivity testing) )

Question 19

How are gram stains useful in determining pathogen responsible for infection?

Answer 19

This test can divide all bacteria into 2 main groups (gram+ and -) by colour alone. Staining also reveals the structure (cocci vs. bacillus) and it can also stain WBC (an indicator for the body’s response against an infection).

Some bacteria like the ones that cause TB do not stain well

Unfortunately, viruses are far too small to be visible or stained using this technique.

Question 20

How are laboratory cultures useful in determining pathogens responsible for infection?

Answer 20

This is the best method for revealing the pathogen causing the infection. Gram stains cannot provide an exact species, while culture tests can.

The organism is grown in different environments and its biochemical profile is determined.

We also need to be aware of possible contamination issues

Question 21

What is MALDI-TOF MS and how is it useful?

Answer 21

MALDI-TOF MS is a technique that vapourizes bacterial samples with laser. The ionized proteins and macromolecules are analyzed by a computer and can determine the microorganism in the sample. This technique is a version of mass spectrometry applied to biological study

Question 22

How is sensitivity testing useful in treating infections?

Answer 22

These tests determine which antibiotics the organism is susceptible to (helps us predict resistance and prescribe accordingly)

It is based on the minimal inhibitory concentration of a given pathogen sample.

Clinically, one must take into account the site of infection and penetration of the antibiotic before prescribing any agent.

Question 23

Why is immunology testing (serology) useful?

Answer 23

Useful when the organism cannnot be cultured or treatment has already begin

ex. Mycoplasma pneumonia is hard to grow, by we can use serology to determine pathogen from sample

Question 24

What is antibody testing?

Answer 24

Detects precesnse of antibodies directed against the pathogen

Question 25

What is antigen detection?

Answer 25

Detects the presence of an antigen in the serum, urine, CSF, and etc.

ex. bacterial, fungal, or viral

Question 26

What is polymerase chain reaction (PCR)?

Answer 26

Detects very low amounts of specific DNA (viral, bacteria) in clinical specimens

Question 27

What is Empiric Antibiotic Choice?

Answer 27

It is an educated guess about what is the most appropriate antibiotic given host and drug factors, but without knowing pathogen or susceptibility

Question 28

What is prophylaxis?

Answer 28

It is an approach to using antibiotics to prevent an infection.

Prophylaxis is sometimes not the best therapeutic choice (giving viral infection antibiotics just in case it is the bacterial form)

Question 29

When are antibiotics indicated?

Answer 29

Some conditions like pneumonia, wound infection, UTIs are obviously bacterial, but others are less clear. In ambigous situations use the following factors to determine whether antibiotics are indicated:

Age, other illnesses, travel history, etc. (helps us narrow down possible pathogens)

Examine chance that symptoms could be due to other things

Consider liklihood of viral infection

Consider urgency of the situation

Question 30

When are lab specimens needed?

Answer 30

These specimens can be taken before giving antibiotics to patients. This allows medical professionals to determine susceptibility

Question 31

How is local pathogen data useful in prescribing the most appropriate agents?

Answer 31

Many times antibiotics need to be started without knowing the causative organism.

Knowing the most common local pathogens can help medical professions be more confident in their chosen antibiotic. Antibiograms show this data well

Question 32

What is the difference between drug allergy and irritation?

Answer 32

Drug allergies affect multiple systems and can be life-threatening

Drug irritation most commonly affect the skin and form rashes.

Incorrect classification of irritation under allergies could prevent the use of an antibiotic in an emergency

Question 33

How to determine what antibiotics are the most appropriate?

Answer 33

Consider patient allergies (are they real)

Penetration issues

Location of infection

Consider side effects

Bacteriostatic vs. bacteriocidal

Consider cost

Frequency and route of administration

Narrow vs. broad spectrum

Question 34

Are antibiotic combination therapies useful?

Answer 34

One agent is sufficient in most cases (only use more than one antibiotic in more complex cases)

But can be used in especially severe infections that have multiple pathogens or for agents that act synergistically

Question 35

What is the disadvantages of using multiple antibiotics?

Answer 35

Increased risk of toxicities

Increased costs

False sense of security

Question 36

What are some important host factors?

Answer 36

Age

Is patient pregnant

Renal or hepatic function

Immunosupressed

Prosthetic devices

Question 37

What is the best route of administration?

Answer 37

In hospital settings, IV formulations are quite common

In outpatient settings, oral formulations are almost the only ones prescribed

Question 38

Are dose regimens for antibiotics the same for all conditions indicated?

Answer 38

No, it is heavily dependent on the infection in question

Sometimes individualized dosing depending on patient factors

Question 39

What is the pharmacist’s role once given a prescription for antibiotics?

Answer 39

Determine indication and usual microorganism associated

Confirm antibiotic choice is appropriate.

Confirm dose and duration is appropriate

Us drug apropriate considering patient factors

Question 40

What can cause antibiotic failure?

Answer 40

Noncompliance (low adherence)

Under dosing

Inaccessible site (imprentratable by agent ex. abcess)

Prosthetic material (lack blood supply, therfore antibiotic efficacy is low)

Resistence

Superinfection (a second infection develops due to the use of an intial antibiotic for the treatment of the original infection)

Some patients simply do not survive