Author(s): Regina LaRocque, Edward Ryan

Respiratory infections are a major reason for returning travelers seeking medical care. Upper respiratory infection is more common than lower respiratory infection. In general, the respiratory infections that affect travelers are like those in non-travelers, and exotic causes are rare. When evaluating a returning traveler with a respiratory infection, inquire about the details of travel, including type of travel and travel destinations.

Infectious Agents

Bacteria

Bacterial causes of respiratory illnesses include Bordetella pertussis, Burkholderia pseudomallei, Chlamydophila pneumoniae, Corynebacterium diphtheriae, Haemophilus influenzae, Mycoplasma pneumoniae, and Streptococcus pneumoniae. Coxiella burnetii and Legionella pneumophila can cause outbreaks and sporadic cases of respiratory illness.

Viruses

Viral pathogens are the most common cause of respiratory infection in travelers. Causative agents include adenoviruses, coronaviruses (e.g., severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2], the cause of coronavirus disease 2019 [COVID-19], and the common human coronaviruses, including types 229E, NL63, OC43, and HKU1), human metapneumovirus, influenza virus, measles, mumps, parainfluenza virus, respiratory syncytial virus, and rhinoviruses. Other viruses of special concern to travelers include Middle East respiratory syndrome (MERS) coronavirus and highly pathogenic avian influenza viruses; consider these viruses in travelers with new-onset respiratory illness, including people requiring hospitalization, when no alternative cause has been identified.

Coronaviruses

Include COVID-19 in the differential diagnosis of travelers who develop evidence of upper or lower respiratory tract symptoms, anosmia, diarrhea, fever, myalgia ≤14 days after international travel, and consider referring positive specimens for genomic sequencing. Travelers can be a source of transmission of new SARS-CoV-2 variants from one geographic region to another (see Sec. 5, Part 2, Ch. 3, COVID-19, and CDC's COVID-19 website.

Include MERS in the differential diagnosis of travelers who develop fever and pneumonia ≤14 days after traveling from countries in or near the Arabian Peninsula. Contact with a confirmed or suspected case of MERS, or with health care facilities in a MERS transmission area, is of special concern, even in the absence of confirmed pneumonia (see Sec. 5, Part 2, Ch. 14, Middle East Respiratory Syndrome / MERS, and CDC's MERS website.

Avian Influenza Virus

Consider a diagnosis of highly pathogenic avian influenza virus (e.g., H5N1, H7N9) in patients with new onset of severe acute respiratory illness requiring hospitalization when no alternative cause has been identified. A history of recent (≤10 days) travel to a country with confirmed human or animal cases—especially if the traveler had contact with poultry or sick or dead birds—increases the likelihood of the diagnosis (see Sec. 5, Part 2, Ch. 12, Influenza, and CDC's Flu website.

Fungi

Fungal pathogens associated with travel include Blastomyces dermatitidis, Coccidioides spp. (see Sec. 5, Part 4, Ch. 1, Coccidioidomycosis), Cryptococcus gattii, Histoplasma capsulatum (see Sec. 5, Part 4, Ch. 2, Histoplasmosis), Paracoccidioides spp., and Talaromyces marneffei (formerly Penicillium marneffei).

Epidemiologic Considerations

Outbreaks can occur after common-source exposures on cruise ships, in hotels, among tour groups, or during international mass gatherings (see Sec. 9, Ch. 10, Mass Gatherings). Histoplasma capsulatum, influenza virus, L. pneumophila, and SARS-CoV-2 are some of the pathogens associated with outbreaks in travelers. Groups having a greater risk for respiratory tract infection include children, older adults, and people with comorbid pulmonary conditions (e.g., asthma, chronic obstructive pulmonary disease [COPD]).

Air Quality

The air quality at many travel destinations might be poor, and exposure to carbon monoxide, nitrogen dioxide, ozone, sulfur dioxide, and particulate matter is associated with health risks, including respiratory tract inflammation, exacerbations of asthma or COPD, impaired lung function, bronchitis, and pneumonia (see Sec. 4, Ch. 3, Air Quality & Ionizing Radiation).

Air Travel

Air pressure changes during ascent and descent of aircraft can result in barotrauma and facilitate the development of sinusitis and otitis media. Direct airborne transmission of pathogens aboard commercial aircraft is unusual because recirculated air passes through a series of filters, and cabin air generally circulates within limited zones or areas of the aircraft. Despite this, COVID-19, influenza, measles, tuberculosis (TB), and other diseases have been transmitted on aircraft.

Transmission could occur via several pathways, including direct droplet spread, direct physical contact, fomites, and suspended small particles (droplet nuclei). Intermingling of large numbers of people in congregate settings (e.g., airports, cruise ships, hotels) also can facilitate transmission of respiratory pathogens.

Seasonality

The peak influenza season in the temperate Northern Hemisphere is during the winter months, typically December–February. In the temperate Southern Hemisphere, peak influenza season runs from late spring or early summer into the fall. Tropical climates have no peak season for influenza, and the risk for infection is year-round. Exposure to an infected person traveling from another hemisphere (e.g., on a cruise ship, as part of a package tour) can lead to an influenza outbreak at any time or place. The potential seasonality of COVID-19 currently is not known; transmission risk might increase during winter months, however.

Tuberculosis

Risk for TB infection among most travelers is low and correlates with the incidence of the disease in the destination country, behavior during travel, and length of stay (see Sec. 5, Part 1, Ch. 22, Tuberculosis).

Clinical Presentation

Most respiratory infections, especially those of the upper respiratory tract, are mild. Upper respiratory tract infections often cause pharyngitis or rhinorrhea. Lower respiratory tract infections, particularly pneumonia, can be more severe. Lower respiratory tract infections are more likely than upper respiratory tract infections to cause chest pain, dyspnea, or fever. Cough is often present in either upper or lower respiratory tract infections.

People with influenza commonly have acute onset of cough, fever, headache, and myalgias. People with COVID-19 might have a similar clinical presentation, but mild disease and asymptomatic infection also are common. Consider pulmonary embolism in the differential diagnosis of travelers who present with cough, dyspnea, tachycardia, or fever and pleurisy, especially those who have recently been on long car or plane rides (see Sec. 8, Ch. 3, Deep Vein Thrombosis & Pulmonary Embolism) or who were recently infected with SARS-CoV-2.

Diagnosis

Give special consideration to diagnosing patients with suspected avian influenza, or illnesses caused by coronaviruses (e.g., COVID-19 or MERS). Identifying a specific etiologic agent in immunocompetent hosts, especially in the absence of pneumonia or serious disease, is not always clinically necessary. If indicated, the following diagnostic methods can be used.

Microbiology. Gram stain and culturing of sputum can help identify a causative respiratory pathogen. Microbiologic culturing of blood, while insensitive, is also recommended as part of a diagnostic work-up.

Molecular Methods. Molecular methods are available to detect certain respiratory viruses including adenovirus, human metapneumovirus, influenza virus, parainfluenza virus, respiratory syncytial virus, SARS-CoV-2, and certain nonviral pathogens.

Rapid Diagnostic Tests. Rapid tests are available to detect some bacterial (e.g., L. pneumophila, Streptococcus pneumoniae, group A Streptococcus), viral (e.g., influenza virus, respiratory syncytial virus, SARS-CoV-2), and fungal (e.g., Histoplasma capsulatum) pathogens.

Treatment

Manage travelers with respiratory infections similarly to non-travelers, but evaluate those who are severely ill for diseases specific to their travel destinations and exposure history. Most viral respiratory infections are mild and do not require specific treatment. Treat travelers with pneumonia of uncertain etiology, as established by the presence of an infiltrate on chest radiography, with antibiotics in accordance with existing guidelines for community-acquired pneumonia. For travelers with influenza who have severe disease or who are at greater risk for complications, treat with antiviral medications. Antiviral treatment for influenza is most effective if begun ≤48 hours of symptom onset. Treat people with COVID-19 per current guidance.

Prevention

Vaccines are available to prevent a number of respiratory diseases, including COVID-19, diphtheria, H. influenzae type B (in young children), influenza, measles, pertussis, S. pneumoniae, and varicella. Unless contraindicated, travelers should be up to date with COVID-19 and influenza vaccines and other routine immunizations, especially against S. pneumoniae.

Preventing respiratory illness while traveling might not be possible, but travelers can follow common-sense measures, including adhering to current recommendations regarding advisability of travel and any indicated precautions (e.g., mask wearing, physical distancing); minimizing close contact with people who are coughing and sneezing; avoiding live animal markets; frequently washing hands, either with soap and water or alcohol-based hand sanitizers containing ≥60% alcohol when soap and water are not available; and, if the traveler has a preexisting eustachian tube dysfunction, using a vasoconstricting nasal spray immediately before air travel, which might decrease the likelihood of otitis or barotrauma.

Health care workers should use appropriate infection-control measures while managing any patient with a respiratory infection.