Malaria cases in the United States hit a 40-year high in 2011, federal health officials reported.
There were 1 925 cases of malaria that year, the highest number since 1971 - a 14% increase from 2010 to 2011.
Five people died from malaria or associated complications in 2011, according to a US Centre for Disease Control and Prevention report.
Nearly 70% of the cases were imported from countries in Africa, and nearly two-thirds (63%) of those cases were acquired in West Africa. India was for the first time the country from which the most cases were imported, officials said.
CDC director Dr Thomas Frieden said: "Malaria isn't something many doctors see frequently in the United States, thanks to successful malaria elimination efforts in the 1940s.
"The increase in malaria cases reminds us that Americans remain vulnerable and must be vigilant because our world is so interconnected by travel."
Malaria is caused by a parasite transmitted by the bite of infected mosquitoes. There were about 219 million cases of malaria worldwide in 2010 and about 660 000 deaths from the disease.
Common symptoms of the disease include fever, headache, back pain, chills, increased sweating, muscle pain, nausea, vomiting, diarrhoea and coughing.
Untreated infections can quickly lead to a coma, kidney failure, respiratory problems and death, the CDC said.
The director of CDC's division of parasitic diseases and malaria, Dr Laurence
Slutsker, said: "Malaria is preventable. In most cases, these illnesses and deaths
could have been avoided by taking recommended precautions."
Americans who travel to regions where malaria is present can protect themselves by taking anti-malarial drugs and by using insect repellent, insecticide-treated bed nets and protective clothing.
"We have made great strides in preventing and controlling malaria around the world. However, malaria persists in many areas and the use of appropriate prevention measures by travellers is still very important," Slutsker said.
The findings were published in the issue of the CDC's Morbidity and Mortality Weekly Report.
The US Centres for Disease Control and Prevention has more about travel and malaria.