A lower respiratory infection is an infection that affects the airways and lung tissue below the voice box. This includes the windpipe, the branching airways inside the lungs (bronchi and bronchioles), and the tiny air sacs where oxygen enters your bloodstream. Pneumonia, acute bronchitis, and bronchiolitis are all types of lower respiratory infections, and together they rank among the leading infectious causes of death worldwide.
Where the Infection Happens
Your lower respiratory tract starts at the windpipe and extends deep into the lungs. The windpipe splits into two main bronchi, one for each lung, which branch into progressively smaller tubes called bronchioles. At the very end of these bronchioles sit clusters of tiny air sacs called alveoli, where your blood picks up oxygen and releases carbon dioxide. A lower respiratory infection can target any of these structures, and the deeper the infection reaches, the more serious it tends to be.
Types of Lower Respiratory Infections
The three main types are bronchitis, bronchiolitis, and pneumonia. They differ in which part of the airway is affected and how sick they can make you.
- Acute bronchitis is inflammation of the bronchi, the larger airways. It usually starts with a persistent cough that may produce discolored mucus, along with a mild fever. Most cases are caused by viruses, and antibiotics provide little benefit.
- Bronchiolitis is inflammation of the bronchioles, the smallest airways. It primarily affects infants and young children and is most often caused by respiratory syncytial virus (RSV). Because young children have such small airways, even mild swelling can make breathing difficult.
- Pneumonia is infection of the lung tissue itself, including the alveoli. It fills the air sacs with fluid or pus, which interferes directly with oxygen exchange. Pneumonia is the seventh leading cause of death in the United States and accounts for the vast majority of deaths from respiratory infections globally.
Common Symptoms
Lower respiratory infections share a core set of symptoms: cough, fever, chest pain, rapid breathing, and mucus production. The specifics vary by type. Acute bronchitis typically starts with a cough that may become productive, meaning you cough up mucus that can look yellow or green. Fever tends to be moderate.
Pneumonia adds shortness of breath to the picture. You may feel winded doing things that normally wouldn’t tire you, and chest pain often worsens when you breathe deeply or cough. Fever can spike higher with pneumonia than with bronchitis, and fatigue is often more pronounced. In older adults, confusion or a drop in body temperature can sometimes be the most noticeable sign rather than a high fever.
What Causes These Infections
Viruses are the most common cause. Respiratory syncytial virus, influenza, parainfluenza, adenovirus, rhinovirus, and coronaviruses all infect the lower respiratory tract. Most cases of acute bronchitis and nearly all cases of bronchiolitis are viral.
Bacteria cause many cases of pneumonia. The most frequent culprits are Streptococcus pneumoniae (the “pneumococcus”) and Haemophilus influenzae. Staphylococcus aureus and various gut-related bacteria can also be responsible, particularly in people with weakened immune systems or those who develop infections during a hospital stay. Tuberculosis remains a major cause of lower respiratory infection in many parts of the world.
Fungi are a less common cause but can be serious for people with compromised immune systems. Certain fungal infections are also tied to geography. Histoplasmosis, for example, is more common in the Ohio and Mississippi River valleys, while coccidioidomycosis clusters in the southwestern United States.
Who Is Most at Risk
Age sits at both ends of the risk spectrum. Infants and young children have immune systems that are still developing, and their small airways make them more vulnerable to infections that cause swelling. At the other end, adults over 65 face the highest risk of dying from respiratory infections. The immune system weakens with age, and older adults are more likely to have other health conditions that compound the danger.
Chronic lung disease (including COPD and asthma), heart disease, diabetes, and chronic kidney disease all raise the risk of a lower respiratory infection becoming severe. A weakened immune system, whether from medication, cancer treatment, or conditions like HIV, opens the door to a wider range of pathogens that healthy lungs would normally fight off. Pregnancy also increases susceptibility, as does smoking, which damages the airway’s natural defenses.
How It Is Diagnosed
Doctors typically start with a chest X-ray, which can reveal patches of fluid or inflammation in the lungs that point to pneumonia. A pulse oximeter clipped to your finger measures how well oxygen is reaching your blood. If your oxygen levels are low, that suggests the infection is significantly affecting lung function.
Blood tests can identify signs of infection and sometimes pinpoint the specific organism responsible. A sputum sample, where you cough mucus into a cup, can be sent to a lab to check for bacteria. These tests help determine whether antibiotics are needed and, if so, which ones are likely to work.
Treatment and Recovery
Treatment depends entirely on the cause. Since most acute bronchitis is viral, antibiotics are not recommended for it regardless of how long the cough lasts. The CDC notes that over-the-counter medications like cough suppressants, antihistamines, and decongestants can ease symptoms but do not shorten the illness. Most people recover from bronchitis within one to three weeks, though a lingering cough can persist longer.
Bacterial pneumonia does require antibiotics, and how aggressively it’s treated depends on severity. Mild cases can often be managed at home with oral medication. More severe cases, especially in older adults or people with weakened immune systems, may require hospitalization for intravenous treatment and oxygen support. Recovery from pneumonia typically takes one to three weeks for otherwise healthy people, but fatigue can linger for a month or more. Older adults may need several weeks longer to fully recover.
For viral pneumonia and bronchiolitis, treatment is mainly supportive: rest, fluids, fever management, and monitoring oxygen levels. Antiviral medications exist for certain viruses like influenza but work best when started within the first 48 hours of symptoms.
Potential Complications
Most lower respiratory infections resolve without lasting harm, but pneumonia in particular can lead to serious complications. The air sacs sit right next to a dense network of blood vessels, which means bacteria can spill into the bloodstream and cause sepsis, a life-threatening inflammatory response throughout the body.
Fluid can accumulate between the lung and the chest wall, a condition called pleural effusion. If that fluid becomes infected and fills with pus, it becomes an empyema, which may need to be drained. In aggressive infections, lung tissue can die (necrotizing pneumonia), and pockets of pus called lung abscesses can form. Respiratory failure, where the lungs can no longer deliver enough oxygen to the body, is the most dangerous outcome and requires emergency treatment.
Prevention
Vaccination is the most effective way to reduce your risk. Pneumococcal vaccines protect against the most common bacterial cause of pneumonia and are recommended for all adults 50 and older, as well as younger adults with chronic lung disease or other risk conditions. Annual flu shots lower the chance of influenza-related pneumonia. RSV vaccines are now available for older adults and pregnant people, helping protect both the individual and, in the case of pregnancy, the newborn.
Beyond vaccination, basic hygiene measures matter. Frequent handwashing, avoiding close contact with sick individuals, and not smoking all reduce your exposure and keep your lungs’ natural defenses intact. For people with chronic conditions like asthma or COPD, staying current on all recommended vaccines is especially important since respiratory infections can trigger flare-ups that compound the damage.