22.2 Bacterial infections of the respiratory tract  (Page 14/21)

Diagnosing rickettsial infection by cultivation in the laboratory is both difficult and hazardous because of the easy aerosolization of the bacteria, so PCR and ELISA are commonly used. Doxycycline is the first-line drug to treat acute Q fever. In chronic Q fever, doxycycline is often paired with hydroxychloroquine .

Bacterial diseases of the respiratory tract

Numerous pathogens can cause infections of the respiratory tract. Many of these infections produce similar signs and symptoms, but appropriate treatment depends on accurate diagnosis through laboratory testing. The tables in [link] and [link] summarize the most important bacterial respiratory infections, with the latter focusing specifically on forms of bacterial pneumonia.

Key concepts and summary

• A wide variety of bacteria can cause respiratory diseases; most are treatable with antibiotics or preventable with vaccines.
• Streptococcus pyogenes causes strep throat , an infection of the pharynx that also causes high fever and can lead to scarlet fever , acute rheumatic fever , and acute glomerulonephritis .
• Acute otitis media is an infection of the middle ear that may be caused by several bacteria, including Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis . The infection can block the eustachian tubes, leading to otitis media with effusion .
• Diphtheria , caused by Corynebacterium diphtheriae , is now a rare disease because of widespread vaccination. The bacteria produce exotoxins that kill cells in the pharynx, leading to the formation of a pseudomembrane ; and damage other parts of the body.
• Bacterial pneumonia results from infections that cause inflammation and fluid accumulation in the alveoli. It is most commonly caused by S. pneumoniae or H. influenzae . The former is commonly multidrug resistant.
• Mycoplasma pneumonia results from infection by Mycoplasma pneumoniae ; it can spread quickly, but the disease is mild and self-limiting.
• Chlamydial pneumonia can be caused by three pathogens that are obligate intracellular parasites. Chlamydophila pneumoniae is typically transmitted from an infected person, whereas C. psittaci is typically transmitted from an infected bird. Chlamydia trachomatis , may cause pneumonia in infants.
• Several other bacteria can cause pneumonia in immunocompromised individuals and those with cystic fibrosis.
• Tuberculosis is caused by Mycobacterium tuberculosis . Infection leads to the production of protective tubercles in the alveoli and calcified Ghon complexes that can harbor the bacteria for a long time. Antibiotic-resistant forms are common and treatment is typically long term.
• Pertussis is caused by Bordetella pertussis . Mucus accumulation in the lungs leads to prolonged severe coughing episodes (whooping cough) that facilitate transmission. Despite an available vaccine, outbreaks are still common.
• Legionnaires disease is caused by infection from environmental reservoirs of the Legionella pneumophila bacterium. The bacterium is endocytic within macrophages and infection can lead to pneumonia, particularly among immunocompromised individuals.
• Q fever is caused by Coxiella burnetii , whose primary hosts are domesticated mammals (zoonotic disease). It causes pneumonia primarily in farm workers and can lead to serious complications, such as endocarditis.

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