The CDC recommendation came after studies revealed that whooping cough, which fell to an all-time low of 1000 cases in the United States in 1976, has increased 25-fold in the three decades since then.

During the 1930s and 1940s, about 200,000 people a year got whooping cough, and about 4,000 a year died from it. Whooping cough is especially dangerous for infants because it attacks their fragile lungs and causes serious breathing problems.

Whooping cough immunizations were introduced in the 1940s, and the number of of whooping cough cases nationally fell to a low of about 1,000 a year in 1976. But now the U.S. Centers for Disease Control and Prevention reports that whooping cough is the only vaccine-preventable disease that is increasing in the U.S.

According to medical experts, the increase has probably resulted from waning immunity to whooping cough in adolescents and adults because their childhood shots for whooping cough wear off over time. And because there has been so little media attention to whooping cough in recent years, many people think whooping cough has been wiped out.

Last year, more than 25,000 cases of whooping cough were reported in the United States. But these cases may represent only a small fraction of actual illnesses because symptoms of whooping cough resemble those of the common cold. As a result, many cases of whooping cough are not reported.

Many people who have whooping cough (pronounced (HOO-ping cough) never develop the telltale ?whoop? that often occurs during coughing spells in patients with serious cases.

Patients with whooping cough can remain contagious for up to three weeks after they contract it. Anyone who has whooping cough should take great care to stay away from infants and persons with respiratory problem, because serious consequences can result.

Deaths from whooping cough are rare: just 56 people died of whooping cough in 2001, 2002 and 2003 combined, according to the CDC. But most were under the age of six months.