Pediatric Hypersensitivity Pneumonitis Clinical Presentation

Updated: May 20, 2016
  • Author: Harold J Farber, MD, MSPH; Chief Editor: Girish D Sharma, MD, FCCP, FAAP  more...
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A comprehensive environmental history and high index of suspicion are critical for diagnosis. Hypersensitivity pneumonitis (HP) should be considered in patients with chronic or recurrent cough, shortness of breath, or a history of recurrent acute respiratory symptoms without definite infectious triggers.

Inquire about specific exposures; the patient may not volunteer them. Because bird fancier’s lung is the most common hypersensitivity pneumonitis in children; be sure to ask about bird exposure. Contact may not necessarily be in the home and may not be obvious. Exposures may be in or near the home, at school, at play locations, as a part of hobbies, at the place of employment, or anywhere else the child spends time. Repeated questioning, home inspection, and/or inspection of sites where the child spends time may be needed to identify the causative antigen.

As new exposures leading to hypersensitivity pneumonitis continue to be identified, exposure to any area likely to contain high concentrations of respirable organic antigens, particularly fungal or avian antigens, should lead one to include hypersensitivity pneumonitis in the differential diagnosis.

Clues that suggest the diagnosis of hypersensitivity pneumonitis are as follows:

  • History of recurrent pneumonia, particularly with regularity or a pattern

  • Other people at home or school who have similar symptoms

  • Development of respiratory symptoms after the patient moves to a new home or new school

  • Improvement of symptoms when the patient is away from home or school for an extended period

  • Contact with birds

  • Water damage to the patient's home or school facility

  • Use of a hot tub, sauna, or swimming pool

The key to diagnosing hypersensitivity pneumonitis lies in a detailed history. The clinician has to maintain a high index of suspicion. Reaching the diagnosis can be difficult because symptoms are often nonspecific and the available diagnostic tests are imperfect. Taking appropriate, effective action to eliminate the inciting exposure can prevent substantial pulmonary morbidity and mortality.

A multicenter study was designed to derive and validate a clinical prediction rule in adult patients who presented with a pulmonary condition for which hypersensitivity pneumonitis was in the differential diagnosis. The study noted 6 significant predictors of a final diagnosis of hypersensitivity pneumonitis, as follows: [41]

  • Exposure to a known offending antigen

  • Positive precipitating antibodies to the offending antigen

  • Recurrent episodes of symptoms

  • Inspiratory crackles upon physical examination

  • Symptoms occurring 4-8 hours after exposure

  • Weight loss

Although the associated probabilities of hypersensitivity pneumonitis from these predictors cannot be generalized to children who have a different spectrum of illnesses, they are useful questions to incorporate into the history.

Manifestations of hypersensitivity pneumonitis are classified as acute, subacute, or chronic. These classifications should be considered as points along a spectrum of illness rather than clearly delineated, discrete types of illness. [42] This classification is based on clinical presentation, not histopathology. In patients with acute disease, a temporal relation between the respiratory symptoms and antigenic exposure can usually be identified. In cases of subacute or chronic exposure, the association between antigenic exposure and development of disease may not be obvious.



Acute hypersensitivity pneumonitis is characterized by the abrupt onset (4-6 h after exposure) of fever, chills, malaise, nausea, dry cough, chest tightness, and dyspnea. Physical examination may reveal tachypnea and fine crackles localized to the lung bases; wheezing is unusual. The presentation is easily confused with that of an infectious pneumonia. Removal from exposure usually results in resolution of symptoms within hours to days.

Subacute hypersensitivity pneumonitis is characterized by the gradual development of productive cough, dyspnea, fatigue, anorexia, weight loss, and low-grade fever. Physical examination and chest auscultation may reveal tachypnea and diffuse crackles. In patients with very severe disease, cyanosis may be present. [1] Resolution of disease may take weeks to months after removal from exposure.

Chronic hypersensitivity pneumonitis may be difficult to diagnose in its early stages. A chronic cough with normal physical examination findings may be the first presentation. Over time, the disease may progress to dyspnea, fatigue, weight loss, and exercise intolerance. Auscultation of the chest may reveal crackles. An “inspiratory squawk” or “chirping rales” have been described. [43, 44] Digital clubbing may be seen in the advanced stages of the disease.



Types and causes of hypersensitivity pneumonitis in children

A wide spectrum of respirable antigens can trigger hypersensitivity pneumonitis, including avian antigens, rodent antigens, fungi, bacteria, and low molecular weight chemicals. Fungal spores can be present wherever sufficient humidity is present; for example, in piles of moldy hay (farmer's lung), in mold-contaminated ventilation systems (humidifier lung), or in old homes seasonally contaminated by mold (summer-type pneumonitis). [11, 45] Mycobacterial antigens aerosolized by the mist that surrounds an operating hot tub can cause hypersensitivity pneumonitis, colorfully described as hot-tub lung.

Table 1. Commonly Described Causes of Hypersensitivity Pneumonitis [46] (Open Table in a new window)



Source of Antigen


Bird fancier's lung, pigeon breeder's lung, poultry worker's lung, feather duvet lung

Feathers, droppings, serum proteins, intestinal mucins, avian immunoglobulin A


Farmer's lung, Bagasse (sugar cane) lung, mushroom worker's lung, potato riddler's lung, paprika slicer's lung, wine maker's lung

Thermophilic actinomycetes, Aspergillus species, and other fungi in moldy hay or grains; moldy sugar cane; mushroom spores and thermophilic actinomycetes; moldy hay around potatoes, thermophilic actinomycetes, and others; Mucor stolonifer (on moldy paprika pods); B cinerea (noble rot on grapes)

Water-based systems

Humidifier lung, hot-tub lung, sauna taker's lung, lifeguard's lung, sewage pneumonitis, wind instrument lung

Aerosolized molds, endotoxins, mycobacteria, thermophilic actinomycetes, Penicillium species, others

Home environment

Summer-type pneumonitis, mold-contaminated walls, humidifiers, wallpaper

Trichosporon species, mold contamination in older and/or water-damaged homes



Chemical worker's lung, epoxy-resin lung, pyrethrum pneumonitis

Exposure to chemicals in manufacturing, laboratories, spray paints, heated epoxy resins, insecticides

The most common type of hypersensitivity pneumonitis in children is bird fancier's lung. Most often, the bird is a household pet, but, in many cases, the contact may be less obvious. Hypersensitivity pneumonitis has been reported after bird exposure from parental hobbies or occupations, including parental pigeon breeding, [47] pheasant raising, [48] and working on a turkey farm. [49]

Relevant exposures may be from nearby bird activity, with reported cases of hypersensitivity pneumonitis resulting from birds congregating by a backyard pool, [47] goose droppings tracked inside from a contaminated outdoor environment, [50] wild city pigeons nesting just outside the home, [51] birds nesting near the air intake of an air-conditioning system, [52] and neighbors engaged in bird breeding. [53] Live birds are not necessary to cause bird fancier's lung. Exposure to avian antigens from a feather duvet (feather duvet lung) has been linked to hypersensitivity pneumonitis. [54, 55, 10]

Exposure to mold–contaminated moist organic material is a frequent cause of hypersensitivity pneumonitis. Farmer's lung has been reported among children living on farms, especially in children exposed to moist or moldy hay or grains. [56, 57] Summer-type pneumonitis is classically described in the mid and southern parts of Japan, although not exclusively, with onset during summer, resolution by mid autumn, and recurrence the following summer. It is caused by fungal growth (Trichosporon cutaneum) in older wooden homes stimulated by warm, moist summers. [45, 58, 59]

Sources of mold in the child's environment may not be obvious. A compost heap in a play area caused hypersensitivity pneumonitis in one child. [60] Hypersensitivity pneumonitis was diagnosed in a child exposed to moldy hay at a horseback-riding school. [61] A familial cluster of chronic hypersensitivity pneumonitis was caused by mold that collected behind torn wallpaper and beneath worn carpets. [62] Mold that contaminated a basement shower was identified as the cause of hypersensitivity pneumonitis in several children. [63]

Wherever aerosolized water is present, hypersensitivity pneumonitis can occur. Mold contamination of humidifiers has led to the disease in adults and children. [64, 65] A central humidification system that nebulized water into the heating system caused a cluster of hypersensitivity pneumonitis cases in a family. [64] Aerosolized endotoxin generated from a water spray in an indoor swimming pool has been implicated in lifeguard's lung. [66] Hot-tub lung is believed to be a hypersensitivity reaction to contamination of hot-tub water by Mycobacterium avium intracellulare complex or mold in a hot tub. [67, 68]

One case report described antibody-confirmed chronic hypersensitivity pneumonitis to Aureobasidium pullulans, a fungus associated with indoor hydroponics, in a 14 year-old girl. Her lung function normalized after removal of the hydroponics from the home. [69] . Wind instruments, with bacterial and fungal colonization within the instrument, have been implicated as a cause of hypersensitivity pneumonitis. [6, 7]

Low molecular weight chemicals, such as isocyanates (eg, in spray paint and glue), phthalic anhydride (in epoxy resin), and pyrethrum (an insecticide), are thought to cause hypersensitivity pneumonitis by combining with human proteins to form complete antigens. [70]