Skip to main content

Evidence-Based Strategies for Common Clinical Questions

December 2018

Bus Stop Pneumonia: Physiologic or Folklore?

Primary Author: James Odum, MD | Chief Pediatric Resident, Children's Mercy 

Column Editor: Rupal Gupta, MD | Medical Director, Operation Breakthrough Clinic | General Academic Pediatrics | Assistant Professor, UMKC School of Medicine

As the winter season descends upon us, the frequency of clinic and acute care visits for respiratory tract infections, the most common type of infection worldwide, will assuredly reach its annual peak.1 Pediatricians guide parents toward modalities such as handwashing and vaccination to help prevent disease spread. Yet despite reassurances, some parents remain concerned that letting their children play outside when temperatures are low, having them wait outside at the bus stop, or allowing them to drink cold beverages in the winter will cause them to acquire the “common cold,” or worse, pneumonia.2 This folklore presents itself even in historical medical literature, such as A Treatise on the Practice of Medicine, in which noted Philadelphia physician and educator George Bacon Wood stated in the 1866 edition that “vicissitudes of the weather are among the most frequent causes of pneumonia. Sudden exposure to cold, when the body is warm and perspiring, is very apt to induce it.”3 Numerous studies have tested this claim repeatedly over the past century. Inconsistent results have led the modern medical community to remain lukewarm on giving credence to this folklore.

From an epidemiological perspective, the annual incidence of community-acquired pneumonia that results in hospitalization of children is 15.7 cases per 10,000 children, with the highest incidence in children under 2 years old.4 Viral causes are now more often implicated in pneumonia as compared to bacterial causes. The Centers for Disease Control and Prevention (CDC) Etiology of Pneumonia in the Community (EPIC) study, a large multicenter prospective study in children with radiographic evidence of pneumonia, showed that 66% of cases test positive for only a viral etiology; 8% test positive for only a bacterial etiology (from blood, pleural fluid, endotracheal aspirate, or a bronchoalveolar-lavage specimen); and 7% have positive results for both a bacterial and a viral etiology. Respiratory syncytial virus is the most commonly detected pathogen, seen in up to 28% of children with radiographic evidence of pneumonia.

Children, as compared to adults, are more vulnerable to extremes in temperature.  Cold temperatures can adversely affect a child’s immune system and may compromise physical barriers to illness. Even brief exposure to cold, dry air causes vasoconstriction within the respiratory epithelium, as well as impairment in mucociliary clearance.5 Exposing external body surfaces to cold temperatures, such as going outside with wet hair, may also cause local vasoconstriction and lead to a decrease in the temperature of the respiratory epithelium.6 This local vasoconstriction reduces the supply of nutrients and delivery of neutrophils to the respiratory epithelium. Additionally, decreased temperatures of the respiratory epithelium may enhance the ability of some viruses to replicate. Rhinovirus has been shown to replicate best at 33oC (91.4oF), which is noticeably lower than standard body temperatures.6

In supplement of the evidence that cold temperatures may predispose children to developing viral respiratory tract infections, data within the critical care literature shows that hypothermia increases the likelihood of developing bacterial pneumonia.  True in vivo studies exist in the severe brain injury population who have undergone therapeutic hypothermia as part of their trauma management bundle. A meta-analysis evaluating the complications of hypothermia in the adult severe brain injury population found that patients who were therapeutically cooled were twice as likely to contract bacterial pneumonia as patients who were kept normothermic.7 The pediatric literature is less robust, but one study found a statistically significant increase in the rate of bacterial pneumonia in the hypothermia cohort.8 All of these results were matched to a normothermic control population to adjust for ventilator-associated pneumonia as a confounder. At the very least, these results provide evidence that deviation from normothermia increases the susceptibility to bacterial respiratory infections.

Unfortunately, it is unlikely that a prospective study in the pediatric population will ever be conducted to completely answer the question of whether going outside in the cold increases risk of pneumonia. However, as providers are taking the history and performing an exam on the children presenting with respiratory symptoms, they can employ the evidence for a physiologic contribution to any prolonged winter weather exposures as they weigh the likelihood of either a viral or bacterial respiratory infection in their clinic patient. Primary prevention can be targeted at discussions on the importance of vaccinations to prevent pneumococcal, influenza and Bordetella pertussis pneumonia, as well as secondary pneumonia that can be seen as a complication of measles. As for counseling parents on a method of daily prevention during the winter months, simple hand hygiene remains the best available option.9



  1. Cold Temperature and Low Humidity are Associated with Increased Occurrence of Respiratory Tract Infections. Mäkinen TM, Juvonen R, Jokelainen J, Harju TH, Peitso A, Bloigu A, Silvennoinen-Kassinen S, Leinonen M, Hassi J. Respiratory Medicine. 2009; 103:456-462.
  2. Exposure to Cold and Acute Upper Respiratory Tract Infection.* Eccles R, Wilkinson JE. Rhinology. 2014; 53:99-106.
  3. A Treatise on the Practice of Medicine. Wood GB.  6th Ed, Vol II. Philadelphia: JB Lippincott and Co, 1866. 3-33. Google Books Web 15 Nov. 2010.
  4. Community-Acquired Pneumonia Requiring Hospitalization among U.S. Children. Jain S, Williams DJ, Arnold SR, Ampofo K, Bramley AM, Reed C, Stockmann C, Anderson EV, Grijalva CG, Self WH, Zhu Y, Patel A, Hymas W, Chappell JD, Kaufman RA, Kan JH, Dansie D, Lenny N, Hillyard DR, Haynes LM, Levine M, Lindstrom S, Winchell JM, Katz JM, Erdman D, Schneider E, Hicks LA, Wunderink RG, Edwards KM, Pavia AT, McCullers JA, Finelli L. NEJM. 2015; 272: 835-845.
  5. Avoiding Hypothermia, an Intervention to Prevent Morbidity and Mortality From Pneumonia in Young Children. Pio A, Kirkwood BR, Gove S. The Pediatric Infectious Disease Journal. 2010; 29(2): 153-159.
  6. Acute Cooling of the Body Surface and the Common Cold.* Eccles R. Rhinology. 2002; 40:109-114.
  7. The Role of Hypothermia in the Management of Severe Brain Injury: A Meta-Analysis. Harris OA, Colford JM, Good MC, Matz PG. Archives of Neurology. 2002; 59:1077-1083.
  8. Increased Susceptibility to Infection in Hypothermic Children: Possible Role of Acquired Neutrophil Dysfunction. Clardy CW, Edwards KM, Gray JC. Pediatric Infectious Diseases. 1985; 4:379-382.
  9. Infection Prevention and Control in Pediatric Ambulatory Settings. Rathore MH, Jackson MA. Pediatrics. 2017; 140(5):e20172857.