Respiratory tract infections (RTIs) are

infectious disease An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

s involving the lower or upper

respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of conducting air to the alveoli for the purposes of gas exchange in mammals. The respiratory tract is lined with respiratory epithelium as respirato ...

. An infection of this type usually is further classified as an

upper respiratory tract infection An upper respiratory tract infection (URTI) is an illness caused by an acute infection, which involves the upper respiratory tract, including the nose, sinuses, pharynx, larynx or trachea. This commonly includes nasal obstruction, sore throat ...

(URI or URTI) or a

lower respiratory tract infection Lower respiratory tract infection (LRTI) is a term often used as a synonym for pneumonia but can also be applied to other types of infection including lung abscess and acute bronchitis. Symptoms include shortness of breath, weakness, fever, cou ...

(LRI or LRTI). Lower respiratory infections, such as

pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of Cough#Classification, productive or dry cough, ches ...

, tend to be far more severe than upper respiratory infections, such as the

common cold The common cold, or the cold, is a virus, viral infectious disease of the upper respiratory tract that primarily affects the Respiratory epithelium, respiratory mucosa of the human nose, nose, throat, Paranasal sinuses, sinuses, and larynx. ...

Types

Upper respiratory tract infection

The upper respiratory tract is considered the airway above the

glottis The glottis (: glottises or glottides) is the opening between the vocal folds (the rima glottidis). The glottis is crucial in producing sound from the vocal folds. Etymology From Ancient Greek ''γλωττίς'' (glōttís), derived from ''γ ...

or vocal cords; sometimes, it is taken as the tract above the cricoid cartilage. This part of the tract includes the

nose A nose is a sensory organ and respiratory structure in vertebrates. It consists of a nasal cavity inside the head, and an external nose on the face. The external nose houses the nostrils, or nares, a pair of tubes providing airflow through the ...

sinuses Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity. The maxillary sinuses are located under the eyes; the frontal sinuses are above the eyes; the ethmoidal sinuses are between the eyes and the sphenoi ...

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

, and

larynx The larynx (), commonly called the voice box, is an organ (anatomy), organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal ...

. Typical infections of the upper respiratory tract include

tonsillitis Tonsillitis is inflammation of the tonsils in the upper part of the throat. It can be acute or chronic. Acute tonsillitis typically has a rapid onset. Symptoms may include sore throat, fever, enlargement of the tonsils, trouble swallowing, and en ...

pharyngitis Pharyngitis is inflammation of the back of the throat, known as the pharynx. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, difficulty swallowing, swollen lymph nodes, and a hoarse vo ...

, laryngitis,

sinusitis Sinusitis, also known as rhinosinusitis, is an inflammation of the mucous membranes that line the sinuses resulting in symptoms that may include production of thick nasal mucus, nasal congestion, facial congestion, facial pain, facial pressure ...

otitis media Otitis media is a group of Inflammation, inflammatory diseases of the middle ear. One of the two main types is acute otitis media (AOM), an infection of rapid onset that usually presents with ear pain. In young children this may result in pullin ...

, certain

influenza Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These sympto ...

types, and the

. Symptoms of URIs can include

cough A cough is a sudden expulsion of air through the large breathing passages which can help clear them of fluids, irritants, foreign particles and Microorganism, microbes. As a protective reflex, coughing can be repetitive with the cough reflex fol ...

sore throat Sore throat, also known as throat pain, is pain or irritation of the throat. The majority of sore throats are caused by a virus, for which antibiotics are not helpful. For sore throat caused by bacteria (GAS), treatment with antibiotics may hel ...

, runny nose,

nasal congestion Nasal congestion is the partial or complete blockage of nasal passages, leading to impaired nasal breathing, usually due to membranes lining the nose becoming swollen from inflammation of blood vessels. Background In about 85% of cases, nasal ...

headache A headache, also known as cephalalgia, is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of Depression (mood), depression in those with severe ...

, low-grade

fever Fever or pyrexia in humans is a symptom of an anti-infection defense mechanism that appears with Human body temperature, body temperature exceeding the normal range caused by an increase in the body's temperature Human body temperature#Fever, s ...

, facial pressure, and

sneezing A sneeze (also known as sternutation) is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucosa. A sneeze expels air forcibly from the mouth a ...

Lower respiratory tract infection

The

lower respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of conducting air to the alveoli for the purposes of gas exchange in mammals. The respiratory tract is lined with respiratory epithelium as respirator ...

consists of the

trachea The trachea (: tracheae or tracheas), also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all animals' lungs. The trachea extends from ...

(windpipe), bronchial tubes,

bronchiole The bronchioles ( ) are the smaller branches of the bronchial airways in the lower respiratory tract. They include the terminal bronchioles, and finally the respiratory bronchioles that mark the start of the respiratory zone delivering air to ...

s, and the

lung The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...

s. Lower respiratory tract infections (LRIs) are generally more severe than upper respiratory infections. LRIs are the leading cause of death among all

s. The two most common LRIs are

bronchitis Bronchitis is inflammation of the bronchi (large and medium-sized airways) in the lungs that causes coughing. Bronchitis usually begins as an infection in the nose, ears, throat, or sinuses. The infection then makes its way down to the bronchi. ...

and

Influenza Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These sympto ...

affects both the upper and lower respiratory tracts, but more dangerous strains such as the highly pernicious

H5N1 Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus, which causes the disease avian influenza (often referred to as "bird flu"). It is enzootic (maintained in the population) in many bird populations, and also panzoo ...

tend to bind to receptors deep in the lungs. Respiratory system complete en

Diagnosis

Respiratory infections world map-Deaths per million persons-WHO2012

Pulmonary Function Testing Pulmonary function testing (PFT) is a complete evaluation of the respiratory system including patient history, physical examinations, and tests of pulmonary function. The primary purpose of pulmonary function testing is to identify the severity ...

(PFT) allows for the evaluation and assessment of airways, lung function, as well as specific benchmarks to diagnose an array of respiratory tract infections. Methods such as gas dilution techniques and

plethysmograph A plethysmograph is an instrument for measuring changes in volume within an organ or whole body (usually resulting from fluctuations in the amount of blood or air it contains). The word is derived from the Greek "plethysmos" (increasing, enla ...

y help determine the functional residual capacity and total lung capacity. To discover whether or not to perform a set of advanced Pulmonary Function Testing will be based on abnormally high values in previous test results. A 2014 systematic review of clinical trials does not support routine rapid viral testing to decrease antibiotic use for children in emergency departments. It is unclear if rapid viral testing in the emergency department for children with acute febrile respiratory infections reduces the rates of antibiotic use,

blood test A blood test is a medical laboratory, laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a hypodermic needle, or via fingerprick. Multiple tests for specific blood components, such as a glucose ...

ing, or urine testing. The relative risk reduction of

chest x-ray A chest radiograph, chest X-ray (CXR), or chest film is a Projectional radiography, projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most common fi ...

utilization in children screened with rapid viral testing is 77% compared with controls. In 2013 researchers developed a breath tester that can promptly diagnose lung infections.

Treatment

Bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

are

unicellular organism A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

s present on Earth can thrive in various environments, including the human body.

Antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...

s are a medicine designed to treat

bacterial infections Pathogenic bacteria are bacteria that can cause disease. This article focuses on the bacteria that are pathogenic to humans. Most species of bacteria are harmless and many are beneficial but others can cause infectious diseases. The number of t ...

that need a more severe treatment course; antibiotic use is not recommended for common bacterial infections as the

immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

will resolve such infections. This medicine does not effectively treat a viral infection like

and common respiratory tract infections. This is because antibiotics were developed to target features of bacteria that are not present in viruses, and so antibiotics are ineffective as antiviral agents. The CDC has reported that antibiotic prescription is high; 47 million prescriptions in the United States in 2018 were made for infections that do not need antibiotics to be treated with. It is recommended to avoid antibiotic use unless bacterial infections are severe, transmissible, or have a high risk of further complications if left untreated. Unnecessary use of antibiotics could increase antibiotic-resistant infections, affect the

digestive system The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...

, create

allergic reactions Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermatitis, alle ...

, and other intense side effects. A study published in ''

JAMA ''JAMA'' (''The Journal of the American Medical Association'') is a peer-reviewed medical journal published 48 times a year by the American Medical Association. It publishes original research, reviews, and editorials covering all aspects of b ...

'' found that narrow-spectrum antibiotics, such as amoxicillin, are just as effective as broad-spectrum alternatives for treating acute respiratory tract infections in children, but have a lower risk of side effects.

Prevention

Despite the superior filtration capability of N95 filtering facepiece respirators measured in vitro, insufficient clinical evidence has been published to determine whether standard surgical masks and N95 filtering facepiece respirators are equivalent to preventing respiratory infections in healthcare workers. Adults in

intensive care units An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensive care medicine. An inten ...

(ICU) have a higher risk of acquiring an RTI. A combination of topical and systematic antibiotics taken prophylactically can prevent infection and improve adults' overall mortality in the ICU for adult patients receiving

mechanical ventilation Mechanical ventilation or assisted ventilation is the Medicine, medical term for using a ventilator, ventilator machine to fully or partially provide artificial ventilation. Mechanical ventilation helps move air into and out of the lungs, wit ...

for at least 48 hours, and topical

antibiotic prophylaxis Antibiotic prophylaxis refers to, for humans, the prevention of infection complications using antimicrobial therapy (most commonly antibiotics). Antibiotic prophylaxis in domestic animal feed mixes has been employed in America since at least 1970 ...

probably reduces respiratory infections but not mortality. However, the combination of treatments cannot rule out the relevant contribution in the systemic component of the observed reduction of mortality. There is no sufficient evidence to recommend that antibiotics be used to prevent complications from an RTI of unknown cause in children under the age of 5 years old. High-quality clinical research in the form of randomized controlled trials assessed the effectiveness of Vitamin D, another review of poorer quality RCTs addressed the effectiveness of

immunostimulant Immunostimulants, also known as immunostimulators, are substances (drugs and nutrients) that stimulate the immune system usually in a non-specific manner by inducing activation or increasing activity of any of its components. One notable example i ...

s for preventing respiratory tract infections. Despite some uncertainty due to small study sizes, there is some evidence that exercise may reduce severity of symptoms but had no impact on number of episodes or number of symptom days per episode. Viruses that cause RTI are more transmissible at very high or low

relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

; ideal humidity for indoor spaces is between 40 and 60%. Therefore, relative humidity in this range can help lessen the risk of aerosol transmission.

Epidemiology

Respiratory infections often have strong seasonal patterns, with

temperate climate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ra ...

s more affected during the

winter Winter is the coldest and darkest season of the year in temperate and polar climates. It occurs after autumn and before spring. The tilt of Earth's axis causes seasons; winter occurs when a hemisphere is oriented away from the Sun. Dif ...

. Several factors explain winter peaks in respiratory infections, including environmental conditions and changes in human behaviors. Viruses that cause respiratory infections are affected by environmental conditions like

and temperature. Temperate climate winters have lower relative humidity, which is known to increase the transmission of

. Of the viruses that cause respiratory infections in humans, most have seasonal variation in prevalence. Influenza, '' Human orthopneumovirus'' (RSV), and

human coronaviruses Coronaviruses are a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the co ...

are more prevalent in the winter. Human bocavirus and ''

Human metapneumovirus Human metapneumovirus (HMPV or hMPV) is a negative-sense single-stranded RNA virus of the family ''Pneumoviridae'' and is closely related to the avian metapneumovirus (AMPV) subgroup C. It was isolated for the first time in 2001 in the Netherland ...

'' occur year-round,

rhinovirus The rhinovirus (from the "nose", , romanized: "of the nose", and the ) is a Positive-sense single stranded RNA virus, positive-sense, single-stranded RNA virus belonging to the genus ''Enterovirus'' in the family ''Picornaviridae''. Rhinoviru ...

es (which cause the

) occur mostly in the spring and fall, and human parainfluenza viruses have variable peaks depending on the specific strain.

Enterovirus ''Enterovirus'' is a genus of positive-sense single-stranded RNA viruses associated with several human and mammalian diseases. Enteroviruses are named by their transmission-route through the intestine ('enteric' meaning intestinal). Serologic ...

es, with the exception of rhinoviruses, tend to peak in the summer.

References

External links

{{Authority control Infectious diseases Respiratory diseases