Chickenpox is typically a benign, self-limited disease, but serious complications can arise. About 14,000 people are hospitalized because of chicken pox and approximately 100 people die of chickenpox every year. The risk of complications is highest in people with compromised immune systems, newborns, and adults.
After the varicella virus infects the skin, it is not completely eliminated from the body as most viruses are. Instead the virus travels up the nerves to important nerve branching points called ganglia deep in the body where it stays in an inactive, or latent, form. During this time the virus does not replicate. It stays in this latent form for varying amounts of time. Certain triggers may cause the virus to travel back down the nerve to the skin causing painful, burning blisters. This condition is known as shingles, or herpes zoster (although it is not caused by the herpes virus), or varicella zoster, or just zoster. Shingles occur in about 20% of people who have had chicken pox.
The most common complication of chickenpox is secondary bacterial infection of the chickenpox lesions. The bacteria most likely to cause infection are Staphylococcus aureus and Streptococcus pyogenes. The bacteria most commonly cause infections such as impetigo, furunculosis, cellulitis, erysipelas, and lymphadenitis. These infections are superficial, but there is a risk of the bacteria invading the bloodstream and causing bacteremia. People who develop bacteremia are at risk of developing bacterial pneumonia, meningitis, arthritis, osteomyelitis, sepsis, shock, and death. Chickenpox lesions that are secondarily infected should be treated with antibiotics.
The second most common complication of chickenpox involves the neurological system. One of these disorders is called acute cerebellar ataxia which causes progressive irritability, difficulty walking, difficulty with vision, and speech disturbances that persist for days or weeks but normally clear completely over time. Another neurologic complication is varicella meningoencephalitis which causes sudden but transient delirium, seizures, headache, sensitivity to light, and neck pain. These symptoms usually resolve after 24 to 72 hours.
The leading cause of varicella-related morbidity and mortality in adults, pregnant women, and people with compromised immune systems is varicella pneumonia. Approximately 1 in 400 adults who develop chickenpox are hospitalized for varicella pneumonia. Varicella pneumonia is caused by the spread of the virus in the bloodstream to the lungs. Risk factors for developing this complication include:
- Contracting chickenpox at an older age
- A rash that involves a larger number of lesions
- A compromised immune system
- Pregnancy (especially in the third trimester)
- Chronic obstructive pulmonary disease (COPD)
A common complication of chickenpox is a transient hepatitis, or inflammation of the liver. This does not usually cause symptoms and resolves on its own. However, Reye's syndrome is a life-threatening condition that causes liver failure in association with aspirin administration for a viral illness. The incidence of Reye's syndrome has dramatically decreased as parents have learned not to give their children aspirin for a fever.