Cold and Flu Complications: How Dangerous Are These Illnesses?

Most cases of a cold or the flu can be treated at home, with symptoms going away within a week or two. But infections of the upper respiratory tract (nose and throat) and lower respiratory tract (lungs) can lead to moderate or potentially serious health complications.

The Centers for Disease Control and Prevention (CDC) estimates that in the United States, the flu has resulted in between 140,000 and 810,000 hospitalizations each year since 2010 and between 12,000 and 61,000 deaths. (1) While most people with a common cold get better in about a week, those with weakened immune systems, asthma, or respiratory conditions can develop serious complications such as bronchitis or pneumonia, says the CDC (2).

Feeling mildly sick, then better, and then sick again could be a sign of a secondary bacterial infection, a condition that can occur when your immune system is weakened from a mild illness.

“It could be that the immune system got tired and another infection was able to come in,” says David Weitzman, MD, an urgent care physician in South Carolina and a board member of the American Academy of Urgent Care Medicine. “Or you were exposed to a second type of virus or bacteria and got sick again.”

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Certain populations are especially at risk of developing cold- or flu-related complications:

• Adults Age 65 and Older People in this age group account for between 50 to 70 percent of seasonal flu-related hospitalizations and between 70 and 85 percent of seasonal flu-related deaths, according to the CDC. (3)
• Children Under 5 Millions of children get sick with seasonal influenza every year, and thousands require hospitalization; some die. (4)
• Pregnant Women Changes to the immune system, heart, and lungs during pregnancy can raise the risk of severe illness from the flu. The flu may also be harmful to a developing baby. (5)
• Adults With Preexisting Conditions This includes chronic illnesses such as asthma, chronic obstructive pulmonary disease, heart disease, diabetes, and HIV or AIDS. (6)
• American Indians and Alaska Natives Research has shown that these groups experience a disproportionate number of influenza-related hospitalizations compared with the general U.S. population. (7)

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Potential complications of colds and flu include the following:

Bronchitis

Bronchitis, an inflammation of the airways that bring air to and from the lungs, is commonly caused by viruses that cause colds and the flu, according to the National Heart, Lung, and Blood Institute. Bacteria and inhaled irritants can also cause bronchitis. The most common symptom is mucus-laden coughing, with other symptoms including shortness of breath and wheezing. (8)

Dehydration

Colds and the flu can decrease appetite and liquid intake, making it easy to become dehydrated. Diarrhea, vomiting, and fever can also contribute to dehydration, according to the Mayo Clinic (9).

Signs of dehydration in infants or young children may include listlessness, no wet diapers for three hours, a dry mouth and tongue, and no tears when crying. Adults may develop extreme thirst, urinate less, produce darker-colored urine, or feel dizzy, confused, or fatigued. (9)

Severe dehydration is a medical emergency and may require treatment with intravenous fluids. (9)

Ear Infection

“With a cold, you can get ear pain because the eardrum gets inflamed by the viral infection,” says Richard Rosenfeld, MD, a professor and the chair of otolaryngology at the State University of New York Downstate Health Sciences University in Brooklyn. Ear infections are more common in children because the Eustachian tubes (passageways that drain fluids out of the ear) are smaller and can easily become swollen or blocked.

Myocarditis

An inflammation of the middle layer of the heart’s wall (myocardium), myocarditis can be caused by cold or flu viruses, according to the Mayo Clinic. It may begin with mild symptoms, such as fatigue or shortness of breath, but it can lead to arrhythmia (rapid or abnormal heart rhythms), heart attack, or stroke. (10)

Myositis

Viral infections like influenza can cause inflammation that damages muscle fibers, a condition called infectious myositis, according to Harvard Health. Although it can cause muscle aches and muscle tenderness, the main symptom is weakness. Myositis can subside on its own in a few days or weeks, or it can become a chronic condition. (11)

Pericarditis

An inflammation of the saclike tissue surrounding the heart (pericardium), pericarditis is commonly caused by viral infections, according to the American Heart Association. Symptoms include sharp chest pain resembling a heart attack accompanied by fever, weakness, and coughing. Most of the time, the condition resolves itself with little or no treatment, but severe cases require hospitalization and surgery. (12)

Pneumonia

Cold and influenza viruses can lead to pneumonia, a common and potentially life-threatening lung infection. These viruses can lead to viral pneumonia or bacterial pneumonia, the latter of which is usually more serious, according to the American Lung Association. (13)

Symptoms of pneumonia include cough, fever, shortness of breath, rapid and shallow breathing, and nausea and vomiting (especially in small children). If untreated, pneumonia can become severe, with signs such as difficulty breathing, rapid heart rate, and a bluish tint to the lips and nail beds, according to the American Lung Association. (14)

Sinus Infection

Acute sinusitis, an inflammation of the sinuses that causes a buildup of mucus, is most often caused by a cold, according to Harvard Health. The most common symptoms are congestion, headache and facial pain, and discolored mucus, with other signs including loss of smell or taste, cough, bad breath, fever, toothache, and fullness in the ears. (15)

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While both a cold and the flu can cause complications such as sinus and ear infections, complications from the flu are generally more serious and are more likely to lead to conditions that may require hospitalization, like pneumonia, according to the CDC. (16)

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While over-the-counter pain relievers and fever reducers can lessen the symptoms of a cold and the flu, there can be complications.

For instance, taking too much Tylenol (acetaminophen) can damage the liver. According to the Cleveland Clinic, the daily adult dose should not exceed 4 grams per day; for people with liver conditions, the limit is 2 grams per day. (17)

The use of aspirin to reduce pain and fever has been associated with a risk of Reye’s (also called Reye) syndrome in children and teenagers who have a viral infection such as the flu. Reye’s syndrome is a rare but serious condition that causes swelling of the brain and liver damage, according to the Mayo Clinic. (18)

Prescription antiviral drugs for treating the flu may have side effects. The most common side effects of Tamiflu (oseltamivir), for instance, are nausea and vomiting. (19)

Anyone can develop serious complications from the flu, but certain people are at an especially high risk, including men and women over age 65, those with certain chronic health conditions (such as asthma, diabetes, or heart disease), pregnant women, and children younger than 5 (especially those under 2).

The CDC lists a number of emergency warning signs of the flu. For adults, these include the following symptoms: (20)

• Trouble breathing or shortness of breath
• Persistent pain or pressure in the chest or abdomen
• Persistent dizziness, confusion, or inability to rouse from sleep
• Seizures
• Not urinating
• Severe muscle pain
• Severe weakness or unsteadiness
• Fever or cough that improves but then returns or worsens
• Worsening of chronic medical conditions with fever and a worse cough

Emergency warning signs for children with the flu include these:

• Fast breathing or trouble breathing
• Bluish lips or face
• Ribs pulling in with each breath
• Chest pain
• Severe muscle pain (child refuses to walk)
• Dehydration (no urine for eight hours, dry mouth, no tears when crying)
• Not alert or interacting when awake
• Seizures
• Fever above 104 degrees; in children younger than 12 weeks, any fever
• Fever or cough that improves but then returns or worsens
• Worsening of chronic medical conditions

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Most people with the flu recover in a few days to a few weeks without medical care or prescription antiviral drugs, says the CDC. But if your symptoms are severe or you’re in a high-risk group, going without treatment could have serious and potentially life-threatening consequences. Don’t delay: Antiviral medications are most effective when you begin taking them within the first two days of feeling sick, says the CDC. (21)

Additional reporting by Pamela Kaufman.