Causative Agents Of Respiratory Infections

The respiratory system is divided into two tracts. The upper respiratory tract consists of the paranasal sinuses, the nasal cavity, the pharynx, and the epiglottis. The paranasal sinuses are lined with mucous membranes that warm, humidify, and filter the air. The epiglottis seals off the airway during swallowing. The lower respiratory tract consists of the larynx, the trachea, bronchi, bronchioles, lungs, and alveoli. Mucous membranes line the trachea, bronchi, and bronchioles and form the mucociliary escalator. The mucociliary escalator prevents inhaled debris from entering the lungs. Gas exchange occurs in the alveoli, the air sacs in the lungs.

The sinus membranes can become inflamed from allergens or pathogens. This is called sinusitis and can cause sinus congestion if mucus is unable to drain into the nose. Accumulation of mucus in the sinuses can allow bacteria to multiply, causing a sinus infection.

Streptococcus pneumoniae can cause pneumococcal pneumonia. Humans are the only know reservoir of pneumococcal bacteria. Children and the elderly are at the greatest risk of this disease. S. pneumoniae first colonizes the nasopharynx which can then migrate to the lungs. Symptoms of pneumonia cause by S. pneumoniae include high fever, chills, shortness of breath, cough with sputum, and chest pain when inhaling. Pneumonia can be cause by a wide array of infectious agents. Pneumonia resembling S. pneumoniae is used to classify the category of typical pneumonia. Typical pneumonia is caused by bacteria, while atypical pneumonia is caused by viruses. Haemophilus influenzae can also cause pneumonia.

Mycobacterium tuberculosis can cause tuberculosis, also known as consumption. Mycobacterium bovis was historically another common cause until pasteurization made milk products safer to consume. Most infections of M. tuberculosis are latent and do not cause symptoms. Latent tuberculosis cases also do not usually progress to an active case. When an active case of tuberculosis does occur, symptoms include a cough that sometimes contains blood, fever, fatigue, weight loss, and night sweats. Tuberculosis is the fourth leading cause of death form an infectious disease.

Sputum gram stain reports include quantitation of epithelial cells, white blood cells, and any bacteria or fungus seen. Quantitation is reported as rare, few, moderate, or many, though this may vary depending on the laboratory. Bacteria is listed with their gram stain result, and gram positive cocci are described as being in pairs, clusters, or chains. Normal flora is noted, and any potential pathogens are identified in the sputum culture. Identification can be done through the VITEK 2 or MALDI-TOF. Sputum cultures are plated on blood, chocolate, and MacConkey agar. Oxidase and indole are performed on gram negative organisms. An acceptable sputum specimen should contain greater than or equal to 10 white blood cells with mucus and less than 25 epithelial cells per low-power field. Specimens that do not meet this criteria may be contaminated by oropharyngeal flora.