It's a respiratory illness that may start out like a cold. But pertussis, also known as whooping cough, can last for weeks or months.

Whooping cough, also called pertussis, is marked by a severe hacking cough followed by an intake of breath that sounds like "whoop." The illness spreads from person to person through the air, carried by droplets excreted by sneezes and coughs.

Rates of whooping cough in the U.S. continue to climb, according to data from the US Centers for Disease Control (CDC). Over 32,000 cases reported have been reported as of mid-December -- about six times more than there were at this time last year,