Legionella Tb Notes

Legionella

Three epidemiological patterns of disease

1. Outbreaks among previously fit individuals staying in hotels, institutions or hospitals whose showers and cooling systems have been contaminated with the organism

2. Sporadic cases where the source of infection is unknown. Most cases involve middle-aged and elderly men who are smokers (but also seen in children)

3. Outbreaks occurring in immune-compromised patients

The organism

• Gram negative pleomorphic bacteria

• More than 39 species but L.Pneumophila is most frequently implicated in human disease

• Reside in swimming pools, Jacuzzis, air conditioning systems, fountains and domestic and natural water supplies.

• The organism replicates between 20 and 40 degrees

• Infection is spread by aerosol route

• Incubation period is 2-10 days

Pathogenesis

• Outer membrane protein inhibits acidification of phagolysosome

• L. Pneumopila exhibits a potent exoprotease

Signs and symptoms

• Malaise

• Pyrexia

• Fever with rigors

• GI symptoms (half of patients) – D+V, abdo pain

• Haematuria leading to AKI

• Tachypnoeic

• Dry cough that later may become productive and purulent

L.Pneumophilia (Pneumonia)

• A presumptive diagnosis is possible in majority of patients if they have three of following features

  • Prodromal viral-like illness

  • Dry cough, confusion or diarrhea

  • Lymphopenia without marked leukocytosis

  • Hyponatraemia (inappropriate naturetic hormone production)

Investigations

Microbiology

• Sputum or broncheoalveolar lavage fluid cultured (can take up to 3 weeks)

• Rapid diagnosis by immunofluorescence or antigen detection in urine

• Serum antibodies rise after 10-14 days

Biochemistry

• Low serum sodium, raised CRP

Imaging

Chest xray usually shows multi-lobar consolidation sometimes with pleural effusion

Management

• Treatment usually with a macrolide (clarithromycin being drug of choice) combined with rifampacin

• Fluids, analgesia, antipyretics, chest physiotherapy

Tuberculosis

TB causes more deaths worldwide than any other infection.

The HIV pandemic has caused a huge global increase in cases, particularly sub-saharan Africa.

Epidemiology

• Mycobacterium tuberculosis is spread by respiratory droplets

• Transmission occurs from close proximity to an infected individual

• Household contacts of patients with smear positive sputum have a 25% chance of being infected

High-risk groups

• Developing world residents

• Poverty, overcrowding

• Malnourished

• Young or old

• Alcoholic

Pathogenesis

• Following inhalation of organisms, multiplication occurs in subpleural and mid-zone terminal air spaces

• Bacteria ingested by alveolar macrophages survive and spread to local lymph nodes

• Bloodstream spread occurs to lung apices and other organs

• Slow development of cellular immune response leads to tuberculosis granulomata in tissues and cutaneous hypersensitivity to mycobacterial agents

Primary Infection

• Immune response limits damage to localized area of the lung with a primary or ‘Ghon’ focus (calcification may subsequently be visible on a chest X-ray)

• Usually with spontaneous healing

• Dormant infection in 30%

Pulmonary TB

• Majority of cases is due...

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