Atypical pneumonia

Question 1

What are the causative microbes of Atypical pneumonia?

Answer 1

1. Pneumocystis jirovecii
2. Chlamydia pneumoniae
3. Chlamydia psittaci
4. Legionella pneumophila
5. Mycoplasma pneumoniae

Lung abscess

Question 2

What is ATYPICAL pneumonia?

Answer 2

A clinically ‘atypical’ form of pneumonia, which lacks the classic signs and symptoms of pneumonia

It lacks symptoms like e.g lobar consolidation, bronchial breathing.
It causes an interstitial picture on chest x-ray

Atypical pneumonia is pneumonia not caused by one of the more traditional pathogens.

Question 3

Discuss Typical Pneumonia

Answer 3

Typical pneumonia caused by eg Streptococcus pneumoniae

Cannot use a b-lactam antibiotic to treat it as the organisms are resistant, therefore use azithrothromycin or quinolone eg ciprofloxacin.

Question 4

Why won’t routine cultures isolate the microbes that cause atypical pneumonia?

Answer 4

Microbes causing atypical pneumoniae are not easily cultured and therefore routine cultures will not isolate them.

Question 5

What are the most common causative organisms of bacteria? (often intracellular living)

Answer 5

1. Chlamydophilia pneumoniae
   - Causes a mild form of pneumonia with relatively mild symptoms.
2. Chlamydophila psittaci
   - Causes psittacosis.
3. Legionella pneumophila ( gram negative bacilli )
   - Causes a severe form of pneumonia with a relatively high mortality rate, known as legionellosis or Legionnaires’ disease.
4. Mycoplasma pneumoniae
   - Usually occurs in younger age groups and may be associated with neurological and systemic (e.g. rashes) symptoms.
   - No cell wall

Question 6

What is the Chlamydophila pneumoniae?

Answer 6

Obligate intracelluar bacteria
Has a cell wall that does not have peptidoglycan
Bacteria can’t produce its own ATP(adenosine triphosphate), it is an energy parasite

Question 7

What is Chlamydophila psittaci?

Answer 7

Strains of C. psittaci that are most virulent for humans tend to be those associated with psittacine birds

psittacine from the Latin Psittacus, or parrot e.g parrots, parakeets, macaws, cockatoos

Humans who develop psittacosis are commonly:

1. bird fanciers
2. work in poultry farms
3. Abattoirs that process birds
4. pet shops, or veterinarians’ offices.

The organism is usually acquired by inhalation

Question 8

Humans who develop psittacosis are commonly involved in what?

Answer 8

Humans who develop psittacosis are commonly:

1. bird fanciers
2. work in poultry farms
3. Abattoirs that process birds
4. pet shops, or veterinarians’ offices

Question 9

What is legionellae?

Answer 9

Legionella pneumophila is the species that causes 90 % of infections compared to other legionella species.

Gram negative bacillus

Requires special media to grow, will not grow on standard blood plate as it requires cysteine

**Transmitted by infected aerosols

Question 10

What are the environmental sources of Legionella?

Answer 10

1. Warm water
2. Saunas
3. Water cooling towers
4. Geyers
5. Reservoirs
6. Usually found in water

Question 11

What is Mycoplasma pneumoniae?

Answer 11

1. Smallest free-living bacteria
2. Has a cell membrane containing sterols but no cell wall
3. Lack of cell wall means that it is resistant to beta –Lactams eg penicillin, cephalosporin antibiotics
4. Causes mild disease – “walking pneumonia”
5. Laboratory diagnosis – serology – done on serum looking at a fourfold increase in titre
6. Organism is difficult to stain or culture

Question 12

What is pneumocystis jiroveci pneumonia (PCP)?

Answer 12

Pneumocystis is a fungal organism that causes pneumonia predominantly in immunocompromised patients. Eg HIV positive patients
Prior to its discovery as a human-specific pathogen, P. jirovecii was known as P. carinii. (PCP)

Question 13

What is the Epidemiology of pneumocystis jiroveci pneumonia?

Answer 13

-Common in immunocompromised patients esp HIV positive patients ( with AIDS CD4+ <200 cells/μL)

-Also solid organ transplant patients
• Transmission – airborne droplet

Question 14

What is the Microbiology of pneumocystis jiroveci pneumonia?

Answer 14

> Classified as a fungus because RNA is homologous to fungal RNA

> Pneumocystis carinii was classified as a protozoan until late 1980s. The reasons that led to this classification were its morphologic features that were similar to those of protozoa, the lack of ergosterol in its cell membrane and the inability to grow this microorganism on routine laboratory media.

> Four morphological forms – trophozoites, cysts, precysts, sporozoites

> Cyst is diagnostic form and stains with Giemsa and methenamine silver stains
Formerly known as Pneumocystis carinii.

Question 15

What are the four morphological forms of Pneumocystis jiroveci?

Answer 15

Four morphological forms – trophozoites, cysts, precysts, sporozoites

Question 16

What is Pneumocystis jiroveci formerly known as?

Answer 16

Formerly known as Pneumocystis carinii.

Question 17

Why was Pneumocystis carinii classified as a protozoa?

Answer 17

Pneumocystis carinii was classified as a protozoan until late 1980s. The reasons that led to this classification were its morphologic features that were similar to those of protozoa, the lack of ergosterol in its cell membrane and the inability to grow this microorganism on routine laboratory media.

Question 18

What is the Pathophysiology of pneumocystis jiroveci?

Answer 18

Infection in the lung starts with the multiplication of the organism in the alveoli.
As infection progresses, alveoli fill with exudates and inflammatory cells
Desquamation of the alveolar lining cells creates increased permeability of the alveolar capillary membrane and pulmonary oedema.
The inflammatory exudate interferes with gas exchange through the alveolus in the lung

Question 19

What is the clinical presentation of Pneumocystis jiroveci?

Answer 19

1. Subacute to acute onset pneumonia
2. Dyspnea, tachypnea, cyanosis, nonproductive cough, fever
3. Hypoxemia

Question 20

How do we diagnose (or come to a diagnosis) pneumocystis jiroveci pneumonia?

Answer 20

Laboratory Testing is carried out.

1. Fluorescent antibody staining using monoclonal antibodies on induced sputum or bronchoalveolar lavage

Cyst is diagnostic form and also stains with Giemsa and methenamine silver stains

2. PCR ( polymerase chain reaction )– more sensitive than fluorescent antibody staining may be particularly useful on the non-HIV infected immunocompromised host, ( most sensitive test )

( Not available in KZN )

Question 21

What is the prevention and treatment of pneumocystis jiroveci pneumonia?

Answer 21

1. Prevention
   Prophylactic use of oral Tri-metho-prim-Sulfa-methox-azole
2. Treatment

Tri-metho-prim-Sulfa-methox-azole

Question 22

What is a lung abscess?

Answer 22

Lung abscess is necrosis of the pulmonary tissue and formation of cavities containing necrotic debris or fluid caused by microbial infection.

This pus-filled cavity is often caused by aspiration, which may occur during altered consciousness.

During aspiration, bacteria ( usually from mouth) passes past the vocal cords and enters in to the lung causing infection
Alcoholism is the most common condition predisposing to aspiration and lung abscesses.

Problems with swallowing in patients with stroke also predispose to aspiration

Question 23

How does the bacteria get into the lung?

Answer 23

During aspiration, bacteria ( usually from mouth) passes past the vocal cords and enters in to the lung causing infection
Alcoholism is the most common condition predisposing to aspiration and lung abscesses.

Question 24

What is the most common condition predisposing to aspiration and lung abscesses?

Answer 24

Alcoholism

Question 25

Lung abscesses are caused by different organisms. What are they?

Answer 25

> Anaerobic bacteria: Pepto-strepto-coccus, Bacteroides, Fuso-bacterium
Strepto-coccus milleri

> Aerobic bacteria: Staphylo-coccus aureus, Kleb-siella species

> Mycobacteria M. tuberculosis

> Fungi: Asper-gillus species

Question 26

Key features from the ATYPICAL PNEUMONIA lecture.

Answer 26

1. Pneumocystis jiroveci pneumonia- PJP – found in immunocompromised patients eg HIV, a fungal organism.
2. Psittacosis – atypical pneumonia affecting people who work with birds
3. Legionella – gram-negative bacteria found in warm water.
4. Mycoplasma – gram-negative bacteria that does not have cell wall and causes mild pneumonia.