Lower respiratory tract infection

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at August 30, 2016
StartDiseasesLower respiratory tract infection

A lower respiratory tract infection (LRTI) is an acute infection that affects the lungs and airways. Despite the fact that these infections are relatively common and are not life-threatening for most healthy people in countries with adequate health infrastructure, they can be fatal in some instances. There were 150 million cases of LRTIs globally in 2013, leading to approximately 2.7 million deaths.


Definition & Facts

LRTIs form in the part of the respiratory system that includes the trachea (also known as the windpipe), lungs, and primary bronchi. These infections of the lower respiratory tract can be viral infections or bacterial infections, and LRTIs are most prevalent in those with weakened immune systems such as children, the elderly, and anyone diagnosed with an immunodeficiency. The most common infections are:

Symptoms & Complaints

Symptoms may vary depending on the specific type of infection a person has. In most cases, the symptoms will last no more than 21 days.

The most common symptom is a persistent cough that is not explained away by another existing condition. More serious coughing may produce mucus and phlegm. An infection may also manifest itself with one or more of the following indicators:

In the case of the flu, which affects the lower and upper respiratory tracts, there may be headache, stuffy nose, and a sore throat in addition to the above symptoms.


In most instances, the exact cause of the infection cannot be determined. Studies indicate that less than 30% of LRTIs have an identified pathogen. Of those identified, a virus causes an estimated 90% of cases of respiratory tract infections. Viruses are usually indicated in most cases of bronchitis and bronchiolitis. Common viruses that cause an LRTI include influenza virus, parainfluenza virus, adenovirus, coronavirus, and rhinovirus. Viral bronchiolitis, frequently caused by the respiratory syncytial virus, or RSV, is a common condition seen in infants and young children.

Bacterial infections are commonly from the bacteria, Bordetella pertussis, Mycoplasma pneumonia, pneumococcus, or Chlamydophila pneumonia. Most often, a bacterial infection will manifest as pneumonia. Pneumonias are classified as either community-acquired pneumonia or hospital-acquired pneumonia, a type of hospital-acquired infection. Classification depends on where the person with pneumonia was first infected.

An LRTI can be contracted through person-to-person contact. The virus that causes the infection can be found in tiny droplets expelled when someone coughs or sneezes. When the person coughs, the pathogen becomes airborne and can be inhaled by another. An infection may also be spread indirectly when an infected person touches an object that is later handled by another who then contracts the infection.

Diagnosis & Tests

In the initial assessment, the doctor will likely observe the patient’s breathing patterns. The physician may listen to the sounds of the patient’s breathing to determine whether there is inflammation or fluid in the lungs.

A patient that presents with symptoms that can be attributed to an LRTI may have a chest X-ray or a computed tomography (CT) scan to confirm diagnosis and to inspect the condition of the patient’s lungs. The physician may also check the amount of oxygen a person is able to breathe in by checking the oxygen levels in the blood using a pulse oximetry or 'pulse ox test'.

It can be important to differentiate between viral and bacterial infections, as this will affect the course of treatment. Pneumonia, caused by bacteria, may be diagnosed when a patient presents the following symptoms: heart rate that exceeds 100 beats per minute (tachycardia), fever persisting for more than four days, labored breathing or abnormally rapid breathing, or focal chest signs (e.g., crackling, reduced chest expansion, reduced air entry).

When pneumonia is suspected, a physician may test the patient’s blood serum for C-reactive protein (CRP) levels. A test result with >100 mg/L of CRP suggests the patient has pneumonia. Patients who have difficulties swallowing in addition to the typical LRTI symptoms may be diagnosed with aspiration pneumonia.

Treatment & Therapy

Treatment can vary depending on whether the infection is viral or bacterial in nature. If a person has a viral infection, it must simply run its course. The course of treatment only alleviates the accompanying symptoms. It usually only requires home treatment, which includes taking painkillers, remaining hydrated, and getting lots of rest.

Bacterial infections will often require a visit to a physician because they can be treated with antibiotics. Because these infections can impair the airways, treatment may include breathing treatments or another form of ventilatory support.

Many cases of an LRTI can be treated at home, without the need to see a physician. One should see a physician for treatment if he or she has any of the following risk factors:

Additional risk factors, which also require a visit to a physician, exist for those over the age of 65:

Prevention & Prophylaxis

The easiest and most effective way to prevent an LRTI is to practice good hygiene. Washing hands thoroughly and regularly with soap and warm water, especially when sick, is crucial in preventing LRTIs. Anyone that has already been infected should take caution to cover his or her mouth when coughing or sneezing.

The elderly, children, and those with compromised immune systems should take care to avoid exposure to smoke, which can increase one’s risk of developing a respiratory tract infection.

There are some vaccines, such as flu vaccines, pneumococcal vaccines, and tuberculosis vaccines that can help protect against or prevent certain types of respiratory tract infections.