18.2 Respiratory Infections: Tonsillitis, Sinusitis & Mastoiditis, Bronchitis, Community-Acquired & Severe Pneumonia, Bronchiectasis and Paragonimiasis

Why this area matters

The respiratory area of the Microbiology TOS covers:

• upper respiratory tract infections: tonsillitis, sinusitis and mastoiditis;
• community-acquired pneumonia and severe pneumonia with acute respiratory failure;
• bronchopneumonia and bronchitis;
• pulmonary tuberculosis;
• emphysema and bronchiectasis.

Pneumonia is consistently among the leading causes of illness and death in the Philippines, in young children and in older adults alike. Questions ask you to name the likely organism from the clinical setting, interpret Gram stains and special tests, and choose prevention such as pneumococcal, Hib, influenza and pertussis vaccines. Tuberculosis is covered in the next section.

Upper respiratory tract infections

• Tonsillopharyngitis:
  • Most cases are viral (rhinovirus, adenovirus, EBV).
  • Group A Streptococcus (GAS) causes most bacterial cases: fever, tonsillar exudate, tender anterior cervical nodes and no cough. These Centor features guide testing with a rapid antigen test or throat culture.
  • Treat GAS with penicillin or amoxicillin for 10 days to prevent acute rheumatic fever.
  • Peritonsillar abscess causes a "hot potato" voice, trismus and uvular deviation.
  • Diphtheria gives a gray, adherent pseudomembrane that bleeds when removed, with a "bull neck". It is treated with diphtheria antitoxin plus penicillin or erythromycin, and it still causes outbreaks where vaccination coverage is low.
• Acute otitis media and mastoiditis:
  • S. pneumoniae, nontypeable H. influenzae and Moraxella catarrhalis cause acute otitis media and acute bacterial sinusitis.
  • Acute mastoiditis follows otitis media: postauricular pain, swelling and redness, with the auricle pushed down and forward. It can spread to the meninges, the sigmoid sinus (thrombosis), the temporal lobe or the neck (Bezold abscess).
• Sinusitis:
  • Most cases are viral.
  • Bacterial sinusitis is suggested by symptoms lasting 10 days or more, severe onset, or worsening after initial improvement ("double sickening").
  • In a patient with diabetic ketoacidosis or neutropenia, a black eschar on the palate or nasal turbinate suggests mucormycosis.
• Croup: usually parainfluenza virus, with a barking cough, inspiratory stridor and the "steeple sign" on X-ray.
• Epiglottitis: classically H. influenzae type b, now uncommon because of Hib vaccination. It causes a toxic child, drooling and the "thumb sign".
• Pertussis (Bordetella pertussis):
  • Pertussis toxin ADP-ribosylates Gi.
  • Stages are catarrhal, then paroxysmal (whoop, post-tussive vomiting), then convalescent.
  • Lymphocytosis is marked.
  • Diagnosis is by PCR of a nasopharyngeal swab, and azithromycin is the drug of choice for patients and close contacts.
  • Infants are protected through pentavalent vaccine and Tdap in pregnancy.

Bronchitis and bronchiolitis

• Acute bronchitis in healthy adults is usually viral and does not need antibiotics; the cough may last 2 to 3 weeks.
• Acute bronchiolitis in infants is most often caused by respiratory syncytial virus (RSV): wheeze, crackles and hyperinflation.

Organisms of pneumonia

• Bronchopneumonia produces patchy infiltrates centered on bronchioles. It is typical of S. aureus, Gram-negative bacilli and hospital-acquired infection.
• Lobar pneumonia consolidates an entire lobe and is typical of pneumococcus.
• Severe pneumonia with acute respiratory failure means respiratory distress, hypoxemia or shock, and may progress to acute respiratory distress syndrome (ARDS). These patients need ICU care, broad empiric coverage guided by the setting, and cultures.
• Philippine CAP guideline: adults are stratified into low-, moderate- and high-risk groups. The groups are based on vital signs, mental status, extent of chest X-ray findings and decompensated comorbidities, and they decide outpatient, ward or ICU care.

Viral pneumonias

• Influenza (an orthomyxovirus with a segmented RNA genome):
  • antigenic drift (point mutations) causes seasonal epidemics, and antigenic shift (reassortment) causes pandemics;
  • neuraminidase inhibitors such as oseltamivir work best within 48 hours;
  • secondary bacterial pneumonia, especially S. aureus, is a major cause of death.
• SARS-CoV-2 (COVID-19) enters cells through ACE2. Severe cases progress to ARDS and thrombosis.
• RSV, adenovirus and measles also cause pneumonia. Measles pneumonia is a leading cause of measles deaths in malnourished children.

Infections in emphysema and bronchiectasis

• COPD exacerbations are triggered by viruses and by H. influenzae, M. catarrhalis and S. pneumoniae.
• Bronchiectasis is permanent dilation of bronchi after severe or recurrent infection. In the Philippines it commonly follows tuberculosis. It can also come from cystic fibrosis or primary ciliary dyskinesia (Kartagener syndrome).
  • Patients have chronic purulent sputum and hemoptysis.
  • Chronic colonization with Pseudomonas aeruginosa and nontuberculous mycobacteria is common.
  • An aspergilloma may grow in an old tuberculous cavity.

Paragonimiasis: the Philippine lung fluke

Paragonimus westermani (Oriental Lung Fluke)

Paragonimus westermani is endemic in rural mountainous regions of the Philippines, particularly in Sorsogon, Camarines Sur, Albay, Mindoro, Leyte, Samar, and Davao.

• Transmission: Requires two intermediate hosts: the 1st intermediate host is a freshwater snail (Antemelania asperata, formerly Brotia asperata); the 2nd intermediate host is a freshwater mountain crab (Sundathelphusa philippina) or crayfish. Humans acquire infection by eating raw, undercooked, salted or vinegar-marinated freshwater crabs. Metacercariae excyst in the duodenum, penetrate the peritoneal cavity, migrate through the diaphragm, and encapsulate within cystic cavities in the lung parenchyma.
• Clinical Presentation & The TB Mimic: Patients present with chronic cough, dyspnea, pleuritic chest pain, and recurrent hemoptysis producing tenacious, gelatinous, rusty-brown sputum ("chocolate-sauce sputum"). Chest radiography demonstrates infiltrates, nodular opacities, and cavitary lesions that closely mimic pulmonary tuberculosis. In the Philippines, patients presenting with chronic hemoptysis who are repeatedly smear-negative for acid-fast bacilli and non-responsive to anti-TB therapy must be evaluated for pulmonary paragonimiasis.
• Egg Morphology & Treatment: Sputum or stool microscopy demonstrates golden-brown, broadly oval, operculated eggs ($80-120 \times 45-65\text{ um}$) with a flattened operculum sitting within distinct shoulders and a thickened abopercular shell at the opposite pole. Treatment of choice is Praziquantel (25 mg/kg three times daily for 2 days).