This is Gwen Outen with the VOA Special English Health Report.

Influenza can be life-threatening, especially for the very old or the very young. In the United States, a new study raises the estimate of how many people require hospital care related to the flu. Most cases of influenza in the United States usually happen from November until about April, during the colder months.

Researchers from the Centers for Disease Control and Prevention did they study. They looked at hospital records from the flu seasons between 1979 and 2001. They counted flu-related hospitalizations. Doctor William Thompson led the research.

They found that more than 200,000 people are hospitalized each year because of the flu. That is almost two times as many as earlier estimates by the C.D.C.

The researchers say one major reason for the increase is the aging of the population. The number of Americans age 85 and older more than doubled in the last 30 years.

Also, the study included the years in the late nineteen nineties when there were more cases of severe forms of the flu. And the researchers noted a third reason for the higher number of hospitalizations they found. They considered a greater number of flu-related sicknesses to reach the new estimate. The report appeared in the Journal of the American Medical Association.

The highest rates of influenza-related hospitalizations were among people 85 and older. The study found that the risk of hospitalizations increased with age starting at 50. Those least affected were between 5 and 49 years old. Children younger than 5 had rates similar to those among people 50 to 64.

Influenza is a respiratory illness. It attacks the nose, throat and lungs. It causes a high body temperature and muscle aches and makes people feel very tired. It also causes a dry cough and sore throat. The virus spreads through the air when infected people cough or sneeze.

The C.D.C. says most people who get the flu will recover in a week or two. But some people develop life-threatening conditions like pneumonia.

In the United States, health officials say an average of about 36,000 people each year die from influenza. They say the best way to prevent the flu is to get vaccinated each fall before flu season begins.

This VOA Special English Health Report was written by Cynthia Kirk. This is Gwen Outen.

influenza: an acute contagious viral infection characterized by inflammation of the respiratory tract and by fever, chills, muscular pain, and prostration（流行性感冒）

hospitalization: the act of placing a person in a hospital as a patient（住院治疗）

sneeze: to expel air forcibly from the mouth and nose in an explosive, spasmodic involuntary action resulting chiefly from irritation of the nasal mucous membrane（打喷嚏）

pneumonia: an acute or chronic disease marked by inflammation of the lungs and caused by viruses, bacteria, or other microorganisms and sometimes by physical and chemical irritants（肺炎）

vaccinate: to inoculate with a vaccine in order to produce immunity to an infectious disease such as diphtheria or typhus（接种疫苗，种痘 ）