Respiratory infection

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at October 28, 2016
StartDiseasesRespiratory infection

Respiratory infections refer to both upper respiratory tract infections and lower respiratory tract infections. Upper respiratory tract infections and lower respiratory tract infections are typically caused by viruses though bacteria or fungi can also be causes.


Definition & Facts

The upper respiratory tract includes the sinuses, pharynx (area of the back of the throat), and the larynx (area of the voice box and upper neck). The lower respiratory tract includes the trachea (windpipe), bronchi (tubes that carry air to each lung) and the lungs.

Deaths from the flu in the United States are not easy to fully document because they fluctuate wildly from year to year. However, the Centers for Disease Control and Prevention (CDC) estimates that 3,300 to 49,000 die of influenza complications in the United States each year.

Symptoms & Complaints

Allergies and asthma can mimic symptoms of respiratory infections though their cause is not from viral or bacterial pathogens. Upper respiratory tract symptoms usually begin with a tickle in the back of the throat that feels like a minor irritation. The odd feeling in the throat can resolve as other symptoms get worse or the throat may become more irritated, especially if coughing begins.

Nasal congestion and a runny nose (rhinorrhea) are hallmarks of the common cold. Headaches and body aches are also common symptoms.

Upper respiratory tract infections can also be linked to ear infections (otitis) and viral conjunctivitis eye infections. Tonsillitis and laryngitis are also complications of upper respiratory tract infections.

Lower respiratory tract infections can become severe. Influenza infections can become very serious and lead to secondary bacterial infections, such as pneumonia, and make chronic health conditions, such as congestive heart failure, chronic obstructive pulmonary disease (COPD) or diabetes mellitus worse. Many who become infected with the flu may initially feel they have a cold, then the virus begins to quickly cause lower respiratory tract symptoms that can, like pneumonia, progress to life-threatening symptoms.

Symptoms of lower respiratory infections include coughing, shortness of breath, fever, and feeling weak or fatigued. Wheezing is also a common system. Coughing can become very severe and almost constant as infections get worse.

Breathing may become labored to the point where oxygen depletion of the body begins. This can result in hypoxia that leads to visible cyanosis, which is the bluing of the lips and fingernail beds.

Pneumonia and bronchitis may be associated with serious symptoms that affect breathing or cause dehydration. Diarrhea, vomiting, and lack of desire to eat or drink can lead to severe dehydration. Breathing problems and dehydration can lead to hospitalization.


The most prevalent form of upper respiratory tract infection is from the common cold. There are about 200 viral variants that cause it. Rhinovirus strains cause most upper respiratory tract infections; coronavirus, respiratory syntactical virus and parainfluenza viruses are also causes of many infections that cause cold symptoms. Bacterial infections of the sinuses can also mimic many of the symptoms of the common cold. Some sore throats are caused by streptococcal bacteria, which is referred to as streptococcal pharyngitis or strep throat. This infection can spread and cause complications.

There are 51 identified adenoviruses that can cause anything from upper respiratory tract infections, such as the common cold, to lower respiratory tract infections, such as pneumonia. Adenovirus variants can also cause everything from pink eye to gastroenteritis.

Influenza, the flu, is caused by viral strains that affect both the upper and lower respiratory tracts. Influenza viruses are classified into four types labeled A, B, C and D. The yearly flu epidemic that people get vaccinated to protect against is for the A and B types. The A type is further classified into H (of which there are 18 subtypes) and N groups (of which there are 11 subtypes). Influenza B types are classified by their lineage and referred to as B/Yamagata and B/Victoria.

Diagnosis & Tests

Most respiratory infections are diagnosed based on the symptoms and signs a doctor can see and detect with regular office equipment such as a stethoscope and otoscope. Pneumonia can be seen on X-rays. Routine diagnoses are not usually based on determining the actual viral or bacterial strains involved in the infections. That said, testing for the precise viral or bacterial strain involves taking a sample, growing it, and examining it under a microscope. This can take a couple of days or more. Rapid influenza diagnostic tests (RIDTs) are now put to use to help discover influenza infections early so that antiviral drugs may be given early enough to help shorten the duration and severity of the flu.

An infection with the common cold virus can often be differentiated from allergies by a physician. Factors that they take into account are the visual examination of the upper respiratory tract of the nasal membranes and the back of the throat along with symptoms. A cold can present with body aches and a fever, whereas allergies typically do not.

Treatment & Therapy

Many of the treatments and therapies for upper and lower respiratory infections are aimed at relieving symptoms such as coughs, runny noses, body aches, fevers and wheezing. Over-the-counter medications such as ibuprofen, naproxen, and acetaminophen are used to relieve the pain of headaches and body aches as well as work to reduce fevers.

Topical decongestants, such as oxymetazoline, reduce swelling of the nasal passages to clear a stuffy nose, and oral medications, such as phenylephrine and pseudoephedrine, do the same thing. Guaifenesin thins secretions to make coughs more productive, and cough medicines with dextromethorphan help alleviate coughing.

Influenza antivirals given early in the onset of the infection may help shorten the duration and severity of the symptoms. Zanamivir, oseltamivir phosphate and peramivir are the only three FDA-approved influenza antiviral drugs for the common flu variants people get. Amantadine and rimantadine are still used for certain influenza type A strains, but many of the viruses have become resistant to these medications. Antivirals used for treating the flu are not meant to replace getting vaccinated to protect against getting the flu in the first place.

Bacterial infections such as bacterial pneumonia and strep throat are treated with antibiotics. Medications used to treat fungal infections of the respiratory tract include amphotericin B, fluorpirymidins, and chlorquinaldol.

Support in a hospital setting may be involved in treating symptoms of severe infections. Intravenous fluids, oxygen and more powerful medicines are used to help the infected while the immune system clears the virus.

Prevention & Prophylaxis

The best defense against respiratory infections is to live a lifestyle that promotes a healthy immune system and prevents exposure to pathogens as well as getting vaccinated to protect against some influenza and bacterial pneumonia strains. A typical annual influenza vaccine protects against the three major circulating strains for the season. This is called a trivalent vaccine. A quadravilent vaccine that protects against four strains that are expected to be part of the annual flu epidemic is also available.

In addition to a healthy diet, getting regular exercise is also important as well as getting enough daily rest, not using or quitting tobacco, and managing stress appropriately.

Preventative methods for avoiding common infectious diseases that cause respiratory infections includes regular and frequent hand washing, not touching the nose, face, or mouth with hands or fingers, avoiding touching potentially infected surfaces, using hand sanitizers when water and soap are unavailable, and staying away from those who are obviously infected.

Those with weakened immune systems as well as those with chronic diseases, such as congestive heart failure, COPD and diabetes, should be extra careful in avoiding contracting any sort of respiratory infection as the symptoms of the infections can be much more pronounced. The very young and the elderly are also more at risk for serious complications from respiratory infections.