An infection of the lung may be due to a number of bacterial and viral causes, with fungal infections being less common and more frequently seen in immunocompromised patients. Lungs infections may be acute, lasting less than 3 weeks or chronic, persisting for more than 3 weeks. Most lung infections start as a respiratory tract infection, progressing from the bronchi and bronchioles to the lung tissue itself. Some pathogens specifically target the lung tissue and may enter through the respiratory tract but only cause disease once in the lung.
A lung infection is broadly encompassed under the term pneumonia. Inflammation of the lung tissue may be due to an infection or other non-infectious causes. Read more on types of pneumonia. An infection of the lung may be isolated to a single lobe or involve multiple lobes and surrounding parts of the respiratory tract. If left untreated, the infection can spread to the surrounding structures like the pleura or heart, lead to necrosis of the lung tissue and formation of an abscess.
Symptoms of a Lung Infection
The most common symptoms associated with a lung infection is a:
- difficulty breathing
- abnormal breathing sounds
- chest pain
Other signs and symptoms that may be seen include :
- night sweats
- pallor or cyanosis
Most infections isolated only to the lung tend to present with a dry persistent cough. If the infection involves the bronchi as well, then a productive cough would be present. A cough is often the first symptom that presents in a lung infection and in the absence of other symptoms, non-infectious causes of the respiratory system needs to be excluded. Over time this may progress to a productive cough with sputum and even blood being expectorated.
Read more on a persistent cough.
Sputum is any discharge expectorated from the respiratory tract. While the sputum production may be minimal in the early stages if the bronchi are not inflamed, it usually does set it at some point in the course of the disease. At times it can be the first presenting symptom in the absence of a persistent cough.
The sputum color may give some indication of the causative pathogen. For example : currant jelly sputum may be seen in an infection due to Klebsiella species, while a rust-colored sputum may be seen with S.pneumoniae infection. However the sputum should be sent for culture to conclusively identify the causative microogranism. Blood-tinged sputum or even bloody sputum may arise as the infection progresses.
Difficulty breathing (dyspnea) may be seen in both acute and chronic infections. It may vary depending on the extent of inflammation or destruction of the lung tissue, fluid accumulation in the lungs, involvement of the respiratory tract or chest pain, which may reduce the depth of breathing. Difficulty breathing in a lung infection may present as shortness of breath, shallow breathing, rapid breathing or pain upon inspiration.
Abnormal Breathing Sounds
Abnormal breathing sounds may arise as result of mucus and exudate congesting the respiratory tract, lobar consolidation or fluid accumulation within the lungs. A wheeze or stridor is more often associated with pathology in the respiratory tract but may also be present in a lung infection. The typical sounds associated with a lung infection, depending on the severity, includes crackles which may sound like a bubbling nose or even a grating noise in the case of a lung abscess.
Chest pain may not always be present in every case of a lung infection, When it does occur, it is often initially related to persistent coughing leading to muscle strain (chest wall pain) and irritation of the respiratory passages. As the infection progresses, chest pain may occur upon inspiration and later become constant. The pain could also be a result inflammation of the pleura (pleuritis/pleurisy), the lining surrounding the lung.