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Medical Microbiology > 9. Pneumonia > Flashcards

9. Pneumonia Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

What is pneumonia?

A
  1. At the basic level, it is something infecting and growing in the lungs.
  2. It is an old disease but still a big problem.
  3. Community-based pneumonia is often quite treatable.
  4. around 450 million cases per year.
  5. Major cause of death in all age groups.
  6. Increasing AMR in some pneumonia causing pathogens but not all.
  7. Problems with immunosuppressed and elderly patients as well as co-morbidities.
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2
Q

How is pneumonia defined and diagnosed?

A
  1. Presence of respiratory system like a cough and at least one other symptom like chest pain.
  2. At least 1 systemic symptom like fever.
  3. No other explanation for symptoms.
  4. X-ray is needed for true diagnosis. Bacterial growth, mucus and inflammation create a cloudiness in the lungs.
  5. Community diagnosis is hard due to access to outpatient X-rays and taking too long.
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3
Q

How does pneumonia cause fever?

A
  1. Usually due to high levels of inflammation, especially in gram-negative infections.
  2. It can lead to capillary breakdown and blood leaking into the lungs.
  3. The bacteria can then also get into the blood.
  4. This is now a systemic infection and fever is a systemic symptom.
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4
Q

What does hard diagnosis of community pneumonia lead to?

A
  1. Treatment is based on symptoms without a true diagnosis.
  2. This leads to excessive and preventative use of antimicrobials.
  3. This can contribute to AMR.
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5
Q

What are the 2 ways to classify pneumonia?

A
  1. By place of acquisition.
  2. By pathogen.
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6
Q

What is the classification of pneumonia by place of acquisition?

A
  1. Community acquired pneumonia. (CAP) This is often seasonal and associated with viral infections.
  2. Hospital-acquired pneumonia. (HAP) Symptoms need to start during an >2 days hospital admission.
  3. Ventilator-acquired pneumonia. (VAP) Associated with plastic tubes and the intubation process itself introduces bacteria to the lungs.
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7
Q

What is the classification of pneumonia by pathogen?

A
  1. Different places of acquisition are associated with different pathogens and therefore different antibiotic susceptibility.
  2. Diagnostics to identify the pathogen that causes pneumonia is hard due to the large amounts of commensal bacteria in the throat and mouth.
  3. Treatment is often a stab in the dark
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8
Q

What is Health-care associated pneumonia (HCAP)?

A
  1. Pneumonia with a direct association with healthcare.
  2. But symptoms and treatment occur in the community.
  3. Big worry in hospitals
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9
Q

How are the different pneumonias defined?

A

CAP: symptoms develop in the community and within 48 hours of hospital admission.
HAP: Symptoms develop more then 48 hours after hospital admission.
VAP: Development of HAP associated with endotracheal tube insertion.

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10
Q

How is HCAP defined?

A
  1. Symptoms appear within 90 days of a >2 day hospital admission.
  2. Usually resident of the nursing home or care facility.
  3. attendance of a hospital clinic
  4. Recent IV antibiotics, chemo or wound care.
  5. Normally associated with picking up a colonising bacteria that later causes an infection
  6. HCAP is more likely to occur if you have had antibiotics as it reduces competition from commensals.
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11
Q

What is the epidemiology of CAP?

A
  1. Incidence of CAP in adults annually is 5-10/1000 population.
  2. High hospitalisation rate and produces a large burden on the NHS.
  3. 1%-10% of hospitalised patients require ITU care but mortality is low.
  4. Lung function can reduce very quickly, and low oxygen levels need supplementation and IV antibiotics.
  5. It can deteriorate and kill quickly.
  6. High cost of treatment
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12
Q

What are the risk factors for CAP?

A
  1. Age
  2. Age is also associated with co-morbidities like heart disease, COPD and immune function.
  3. Seasonal due to association with viral infection and bacterial colonisation.
  4. Social factors like overcrowding and poverty and the ethnic groups that are more likely to live in these conditions.
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13
Q

What are the most common causative pathogens for CAP?

A
  1. S. pneumoniae
  2. H. influnzae
  3. However often we don’t know the cause
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14
Q

How does COPD affect CAP?

A
  1. It is very common
  2. The trachea and bronchi are narrowed due to inflammation.
  3. Often caused by smoking and industrial pollutants.
  4. often caused H. Influenzae
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15
Q

How does diabetes affect CAP?

A
  1. Bacteraemia pneumococcal infections.
  2. More likely to enter the blood due to the high levels of sugar in the blood
  3. They are more likely to have burst capillaries.
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16
Q

How does aspiration affect CAP?

A
  1. Increases mucus in the lungs
  2. Reduces the ability to cough and clear the pathogen
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17
Q

How does alcoholism affect CAP?

A
  1. Aspiration of bacteria in mucus
  2. Aspiration of gut bacteria in vomit.
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18
Q

Pneumonia-causing pathogens: S.pneumoniae

A
  1. Most common due to good at evading the immune system due to polysaccharide capsule. Good at getting in the blood.
  2. Gram positive coccus in chains or pairs.
  3. Produces toxins like pneumolysin that cause lung damage.
  4. Cause a large host inflammatory response.
  5. Predisposing factors include: immune deficiencies, steroids, malnutrition, age, and smoking.
  6. Colonises the nasopharynx in ~10% of adults.
  7. Prevention includes vaccination against commonly circulating polysaccharide capsule.
  8. Some immune deficient patients take antibiotic prophylaxis
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19
Q

Resistance in S. pneumoniae

A
  1. Increasing but not a big problem
  2. This is due to not being good at picking up resistance.
  3. S. pneuoniae doesn’t do horizontal gene transfer so relies of low frequency target site mutation
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20
Q

Pneumonia-causing pathogens: H. influenzae

A
  1. Gram negative cocco-bacillus.
  2. Colonises nasopharynx of 75% of healthy humans.
  3. Not as big problem due to successful vaccination.
  4. Although it is gram-negative, it behaves like a gram-positive respiratory pathogen. It can produce ß-lactamses
21
Q

Pneumonia-causing pathogens: S. aureus

A

Rare but severe

22
Q

Pneumonia-causing pathogens: Enterobacterales

A
  1. eg Klebsiella pneumoniae
  2. More common in the elderly
  3. More serious as it can cause haemorrhagic pneumonia
23
Q

What is atypical pneumonia?

A
  1. Pneumonia-like syndromes that don’t respond to penicillin and where no causative organism can be found.
  2. Due to various organisms like legionella
  3. Common features include: resistant to ß-lactams, produce a more diffuse x-ray image, usually difficult to culture
24
Q

What is M. pneumoniae?

A
  1. Common in children and young adults.
  2. Lack a rigid cell wall but have a tri-laminar membrane.
  3. Comes in waves around every 3-4 years.
  4. Droplet transmission
  5. 2-3 week incubation period
  6. Usually a mild disease
  7. Difficult to culture to difficult to treat.
25
Q

What is legionnaire’s disease?

A
  1. Mostly caused by L. pneumophilia
  2. Small gram-negative coccobacilli
  3. Discovered in 1976 after an outbreak in a hotel
  4. It naturally lives in stagnant water like cold water storage tanks or AC units.
  5. Infections is caused by inhalation of aerosols.
  6. Not a lots of person to person transmission everyone just breathe it in from the same source.
26
Q

Why is microbiological diagnosis of pneumonia hard?

A
  1. Hard to collect a sample
  2. lots of organisms in the sample
27
Q

What are the advantages of accurate microbiological diagnosis of pneumonia?

A
  1. Enables use of more narrow-spectrum antibiotics, which reduces overall use and potential side effects.
  2. Decreases the development of resistance
  3. Can allow pathogen identification
28
Q

How are blood cultures used for pneumonia diagnosis?

A
  1. This is the best way to diagnose the causative agent.
  2. It is sensitive but only work if the bacteria gets in to the blood.
  3. Need to be cautious of antibiotics already in the blood.
29
Q

How are urine cultures used for pneumonia diagnosis?

A

Looking for surface structure of bacteria that are broken down and excreted.

30
Q

What is the epidemiology of HAP and VAP?

A
  1. The most common HAI contributing to death.
  2. affects about 1% of patients
  3. VAP has a 25-50% mortality rate and increasing levels of MDR.
  4. VAP usually effects ITU patients who are very sick anyway
  5. Prevention is the key in these infections.
31
Q

What is the most common HAI?

A

UTIs

32
Q

What is the HAP pathogenesis?

A
  1. Mostly gram-negative, so from the person’s own flora
  2. Also, from the environment or from healthcare workers hands.
  3. All about breathing in things from the environment like from sinks or vases.
  4. Risk factors include: sedation, intubation, vomiting, impaired swallowing and long hospital stay.
33
Q

How does sedation increase the risk of HAP?

A

It affects coughing and swallowing, which increases the chance of aspirating the bacteria.

34
Q

How does intubation increase the risk of HAP?

A

The point of intubation can cause bacteria from the gut to be vomited up

35
Q

What usually causes early HAP?

A

Community organism

36
Q

What usually causes late HAP?

A

Antibiotic-resistant hospital opportunistic pathogens

37
Q

Pathogens causing HAP: Pseudomonas aeruginosa

A
  1. Gram negative aerobic bacillus
  2. Widespread in the environment, especially hospitals.
  3. colonises humans and is an opportunistic pathogen.
  4. High levels of antibiotic resistance
  5. Very adaptable
  6. Highly virulent like exotoxins and endotoxins, porins and pili
38
Q

What is serratia?

A
  1. A rare infection
  2. Very common in the lungs
  3. It is like a cross between an enterobacterales and pseudomonas.
  4. It is a gut bacteria that acts like an environmental bacteria.
  5. Rare as a bloodstream infection but can easily be breathed in
39
Q

Can MRSA cause pneumonia?

A
  1. yes and it is highly resistant
  2. Often comes from the healthcare workers
  3. People going in for planned admissions are often screened for MRSA
40
Q

Why is VAP common?

A
  1. Ventilation bypasses the natural mechanisms of immunity that remove bacteria from the lungs.
  2. It allows direct access to the lungs from the outside.
  3. A ventilator can also actively pump bacteria into the lungs
41
Q

How does endotracheal tube placement increase the risk of VAP?

A
  1. Local damage can be caused during the insertion. This increases colonisation and decreases clearance.
  2. Inhalation of aerosols.
  3. Biofilms can form inside the tube and outside the tube at the point it contacts the trachea.
  4. When the tube are flushed or the biofilm gets big enough they burst and go straight into the lungs
42
Q

What antibiotic use can increase the risk of VAP?

A
  1. Broad-spectrum treatment like meropenem.
  2. This kills the commensals which reduces competition
  3. It also selects for resistant variants.
  4. This causes the pathogen to take over.
43
Q

Where can the causative bacteria for VAP come from?

A
  1. Other areas on the patient’s body
  2. From the flora
44
Q

What can happen to some treatable pneumonias?

A

They can mutate or acquire resistance very quickly

45
Q

What are risk factors for VAP?

A
  1. Prolonged ITU stay
  2. Sternal fracture
  3. Previous broad spectrum antibiotic use
  4. colonisation by resistant organisms
  5. Sedation
  6. Age
46
Q

What are some infection control measures to prevent pneumonia transmission in hospitals?

A
  1. Screening swabs
  2. Side rooms on ITU and wards
  3. Barrier nurse
  4. PPE
  5. Hand washing
  6. Screening other patients
  7. Cleaning of equipment
  8. Dedicate nurse
47
Q

What are some prevention measures specifically for VAP?

A
  1. Disinfection of equipment
  2. No routine changing of ventilator equipment
  3. Sterile insertion and suctioning
  4. Nurse head up to prevent secretions pooling
  5. Sedation vacations
  6. Extubate as soon as clinically safe
  7. Selective decontamination.
48
Q

What is selective decontamination and why it is controversial?

A
  1. It is giving patients a cocktail of antibiotics when the enter ITU to decolonised the entire flora from the person.
  2. This is done to minimise the bacteria in the person and therefore the ITU.
  3. Done in the Nederlands which is usually really tight on antibiotic use.
  4. Controversial as it is seen as excessive and unnecessary use of antibiotics and doesn’t always benefit the patient.
  5. The argument is it saves future use of antibiotics and prevents pneumonia in very sick people.

Medical Microbiology (17 decks)

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