Respiratory Tract Infections

Overview of Upper and Lower Respiratory Infections

• Respiratory diseases are among the top causes of death worldwide.
• The respiratory tract is the main portal for pathogen entry, with potentially infectious particles.
• Upper respiratory tract infections (URTIs) are mainly viral, with secondary bacterial or fungal infections.
• Lower respiratory tract infections (LRTIs) can be bacterial, viral, or fungal, and are the fourth leading cause of death.
• URTIs are a common cause of morbidity and account for approximately 9% of all GP visits.
• Both viral and bacterial URTIs produce similar clinical patterns of illness, with symptoms including rhinorrhea, sneezing, sore throat, and fever.
• Sinusitis is characterized by facial pain, nasal obstruction, and nasal discharge, and is most commonly caused by Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus.
• Pharyngitis and laryngitis are usually viral and associated with the common cold, but can also be bacterial or fungal.
• Tonsillitis is mainly caused by common viral strains, but can also be caused by bacterial infections such as Streptococcus pyogenes.
• Diphtheria, caused by Corynebacterium diphtheriae, is a life-threatening upper respiratory infection that can lead to multisystem toxaemia and myocarditis.
• LRTIs are less common than URTIs but often more severe, and can include tracheitis, bronchitis, bronchiolitis, and pneumonia.
• Pneumonia is an inflammation of the lung primarily affecting the alveoli, and can be caused by viral, bacterial, atypical bacterial, or fungal infections. People at risk include infants, young children, the elderly, and those with long-term heart, lung, and kidney diseases, diabetes, cancer, or compromised immune systems.

Respiratory Pathogens Lecture: Upper and Lower Respiratory Infections

• Respiratory diseases are among the top major causes of death worldwide, with lower respiratory infections ranking as the 4th cause of death.
• The respiratory tract is the main portal for pathogen entry, with potentially infectious particles such as viruses, bacteria, and fungi.
• Upper respiratory tract infections (URTI) are mainly viral, while lower respiratory tract infections (LRTI) can be bacterial, viral, or fungal.
• URTIs are a common cause of morbidity, accounting for approximately 9% of all GP visits, and produce similar clinical patterns of illness as LRTIs.
• The common cold is the most common URTI and is caused by rhinoviruses, coronaviruses, parainfluenza viruses, respiratory syncytial virus (RSV), adenoviruses, and influenza viruses.
• Sinusitis is characterized by facial pain, nasal obstruction, and nasal discharge, and is commonly caused by Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus, and other enteric bacteria.
• Pharyngitis and laryngitis are most often due to viral infections associated with the common cold, but can also be caused by bacterial infections such as Streptococcus pyogenes or fungal infections such as candida albicans.
• Tonsillitis is mainly caused by common strains of viruses, but bacterial tonsillitis is most commonly caused by Streptococcus pyogenes.
• Diphtheria is a life-threatening URTI caused by Corynebacterium diphtheriae, which can lead to multisystem toxaemia and myocarditis.
• Tracheitis, bronchitis, bronchiolitis, and pneumonia are common LRTIs, with pneumonia being the most severe and potentially fatal.
• Nosocomial infections of LRTIs are very common, ranking third after urinary tract infections and surgical wound infections.
• Pertussis, or whooping cough, is caused by Bordetella pertussis and is a re-emerging serious respiratory illness affecting infants, children, and occasionally young adults.