Is It a Cold, Influenza, or Pneumonia?

W. Steven Pray, PhD, DPh; Joshua J. Pray


US Pharmacist. 2004;29(1) 

In This Article

Introduction and Etiologies


The human respiratory system is an important defense against inhaled organisms and pollutants. Two mechanisms work together to protect against infections. The goblet cells secrete thick mucus that lines our inner respiratory tract. Ciliated cells move the mucus upward along with embedded inhaled organisms, pollutants, and allergens until it is swallowed or expectorated. However, inhaling the cooler, drier air of winter slowly desiccates the mucus layer until it becomes too thick to be easily mobilized by the cilia. As a result, inhaled organisms are more likely to cause respiratory diseases. Thus, the pharmacist fields many questions about various respiratory diseases during winter months. People often ask their pharmacist to render an opinion about the potential gravity of an infection. Does a person have a cold or "the flu"? Could it be pneumonia? How do the three differ? This month's column will help the pharmacist answer these questions.


The common cold is caused by a host of viral invaders. The primary offenders are the rhinoviruses, but others include Coronavirus, parainfluenza virus, respiratory syncytial virus, adenovirus, echoviruses, and coxsackieviruses. Typically, the common cold is contracted through touching a contaminated object or shaking the hand of an infected person, and then touching the eyes, nose, or intraoral tissues.

Influenza is caused by one of three types of influenza viruses: A, B, or C.[1] It is contracted primarily through inhalation when an uninfected person is close to an infected person who is sneezing or coughing.[2] This year's flu outbreak has already caused severe illness in many patients.

Pneumonia is a clinical diagnosis denoting inflammation of the various units composing the respiratory tract (eg, alveoli, alveolar ducts, bronchioles).[3] Confirmation requires a chest x-ray. It is unusual for otherwise healthy people to contract pneumonia in the same way that they might catch the cold and influenza. Only especially virulent organisms can penetrate host defenses to transmit pneumonia through inhalation. Rather, pneumonia is most often opportunistic, occurring in persons who have chronic illness or other risk factors (eg, advanced age, immunosuppression, alcohol use, immobility, decreased consciousness, malnutrition).[4] The causative agent may be inhaled, injected intravenously, or introduced during an exploratory respiratory tract procedure. The risk of pneumonia is increased when mucokinesis is disrupted. This can occur when a person does not use a humidifier or vaporizer during the dry winter months or when smoking has destroyed or compromised ciliary function. The retained mucus is a fertile breeding ground for inhaled organisms. Infective pneumonia may be either community-acquired or nosocomial in origin.[5,6,7] Community-acquired pneumonia is most often caused by Streptococcus pneumoniae, Group A streptococci, Haemophilus influenzae, Moraxella, Branhamella catarrhalis, Klebsiella species, Staphylococcus aureus, or Pneumocystis carinii).[4] Nosocomial pneumonia is most often caused by Pseudomonas aeruginosa, Klebsiella pneumoniae, or Serratia marcescens. Viral pneumonia may be caused by influenza viruses or Hantavirus.

Noninfective airway inflammation is also called pneumonia. It may occur with the accidental inhalation of oils, such as mineral oil laxatives, or powder, as with babies whose heads are surrounded by a cloud of powder when they are diapered with talcum powder or cornstarch. Inhalation of smoke, environmental or occupational toxins, and aspiration of foreign bodies also cause pneumonia.[8]

Pneumonia may also follow aspiration in persons with various risk factors (eg, gastroesophageal reflux disease, swallowing disorders).[9,10] Infection following aspiration is most often caused by anaerobic cocci, Bacteroides fragilis, or Fusobacterium species.


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