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By Maggie Fox, Health and Science Editor
WASHINGTON (Reuters) - Travelers from Britain, including medical and public health students, brought the new pandemic swine flu to Kenya in the space of a few weeks, researchers reported on Thursday.
Researchers testing out the East African country's new influenza surveillance system said the arrival of the new H1N1 virus let them watch in real time how a virus spreads. On average, one person infected 26 percent of close household-type contacts, they found -- with one infecting a third of his companions.
Ironically, a team of medical students started it, they reported in the U.S. Centers for Disease Control and Prevention's weekly report on death and disease.
"On June 21, 2009, a group of 34 medical students from Nottingham, United Kingdom, flew from London to Nairobi," the team at the Kenya Ministry of Public Health and Sanitation wrote.
"During the 9-hour flight, a male student aged 22 years developed headache and chills. The next day, the group took a five-hour bus trip to Kisumu, a city in western Kenya, where an educational service program had been arranged."
Within days, 70 percent of the students and leaders in the group had flu-like symptoms. Half of them were confirmed to have the H1N1 swine flu virus.
"On June 26, a group of four public health students from London flew to Nairobi and then traveled to Kisumu to work on malaria-related projects," the researchers added.
A 22-year-old woman became ill and infected another of the students -- a 33 percent "attack rate" for the virus.
The researchers think groups like travelling students may be more likely to infect one another than families.
Two individual travelers also brought H1N1 from Britain -- a 5-year-old boy, who infected one other family member, and a 21-year-old student who infected one of four family members.
Knowing infection rates can help officials project how far and fast a new virus such as H1N1 will spread. As every case is not tested, the information can help them extrapolate the true number of infections
In a second report, published in the journal Eurosurveillance, Brett Archer of the National Institute for Communicable Diseases in South Africa and colleagues said swine flu was hitting patients with tuberculosis and the AIDS virus especially hard.
"Our data suggests that common infectious conditions such as HIV and TB may be associated with increased mortality risk," they wrote.
"Even if this elevated risk is found to be relatively small, with the large numbers of HIV and TB infected people in sub-Saharan Africa, this may translate into a substantial public health impact."
(Editing by Peter Cooney)