Complications

Colds rarely cause serious complications. In about 1% of cases, a cold can lead to other complications, such as sinus or ear infections. It can also aggravate asthma and, in uncommon situations, increase the risk for lower respiratory tract infections.

Ear Infections. The rhinovirus infection, a major cause of colds, also commonly predisposes children to ear infections, possibly by obstructing the Eustachian tube, which leads to the middle ear. Viruses may even attack the ear directly. In one study, 74% of patients with rhinovirus colds had pressure abnormalities in their middle ear.

Sinusitis. Between 0.5 - 5% of people with colds develop sinusitis, an infection in the sinus cavities (air-filled spaces in the skull). Sinusitis is usually mild, but if it becomes severe, antibiotics generally eliminate further problems. In rare cases, however, sinusitis can be serious.

Lower Respiratory Tract Infections. The common cold poses a risk for bronchitis and pneumonia in nursing home patients and other people who may be susceptible to infection. Some experts believe that the rhinovirus may play a more significant role than the flu in causing lower respiratory infections in such people.

Aggravation of Asthma. Rhinovirus infections can aggravate asthma in both children and adults and has been reported to be the most common infectious organism associated with asthma attacks. Some studies have reported the common cold being associated with between 33 - 71% of severe asthma episodes. Research suggests that colds promote allergic inflammation and increase the intensity of airway responsiveness for weeks.

Complications of Influenza

In general, the flu is usually self-limited and not serious. About 1% of people who contract the flu are hospitalized. An estimated 36,000 people die each year of influenza-related complications. People at highest risk for serious complications are those over 65 years old and those with other medical conditions. Influenza A is the most severe strain and causes an estimated average of 142,000 hospitalizations per year. Influenza B tends to be milder.

Pneumonia. Pneumonia is the major serious complication of influenza and can be very serious. It can develop about 5 days after viral influenza. More than 90% of the deaths caused by influenza and pneumonia occur among older adults. The growing elderly population will most likely account for an increase in the number of deaths from influenza. Nursing homes patients are especially hard-hit by flu epidemics, with fatality rates as high as 30%. Flu-related pneumonia nearly always occurs in high-risk individuals, such as the following:

• People with weakened immune systems, such as AIDS patients
• Very young children -- [it may be difficult to tell whether pneumonia is related to influenza or caused by respiratory syncytial virus (RSV)]
• Hospitalized patients and anyone with serious medical conditions, such as diabetes, heart, circulation, or lung disorders, particularly chronic lung disease
• Drug abusers who use needles

Combinations of these factors further increase the risk. It should be noted that pneumonia is an uncommon outcome of influenza in healthy adults.

Complications in the Central Nervous System in Children. Influenza increases the risk for complications in the central nervous system of small children. In a 2001 Chinese study, children hospitalized with influenza A had a higher risk for fever related seizures than children with other upper respiratory tract infections. In rare cases, influenza can lead to meningitis and encephalitis (inflammations in the central nervous system). The risks decline after a child turns 1 year old, but are still high in children aged 3 to 5 years old.

Pandemics

Every year, influenza strikes millions of people worldwide. Influenza epidemics are most serious when they involve a new strain against which most people are not immune. Such global epidemics (“pandemics”) can rapidly infect more than one fourth of the world's population. For example, the Spanish flu in 1918 and 1919 killed an estimated 20 million people in the U.S. and Europe and 17 million in India. With modern society’s dependence on airline travel, an influenza pandemic could potentially inflict catastrophic damage on human lives and disrupt the global economy.

The influenza virus mutates rapidly as it moves from species to species. Most Type A influenza strains first develop in migratory waterfowl populations. While most avian influenza (“bird flu”) virus strains are relatively harmless, a few subtypes develop into “highly pathogenic avian influenza” that can be deadly for domesticated poultry and livestock -- and, as recent events have shown, even humans. The medical community is now greatly concerned about the H5N1 bird flu virus, which has infected many people in several countries, and has lead to death. People can become infected from contact with contaminated chickens and pigs. Scientists’ greatest fear is the emergence of a highly contagious virus that spreads from person to person and causes severe illness or death.