It only takes a single one-night stand — unprotected sex, and all — to contract HIV. After that, the virus slowly multiplies, while it destroys the immune system’s protective CD4 cells. It can take weeks before the body can amount a counterattack. It’s during this time period that HIV tests can sometimes come back with a false negative, even though patients are experiencing some of the telltale symptoms of HIV. What’s worse, these symptoms often resemble those of the common flu, making it difficult for doctors to determine which illness they’re looking at. If it’s HIV, preventing further transmission and getting the patient on antiretroviral medications is crucial.

Common symptoms of HIV in its early stages include fever, nausea, vomiting, weight loss, oral ulcers, and swollen lymph glands. With many of these symptoms also being indicative of the common flu, many doctors are unable to differentiate between a normal, relatively harmless flu, and HIV, a new study found. This inability to diagnose based solely on their own observations presents a problem, as blood tests can miss HIV for as many as three months after infection.

“We realized through our four-year STOP HIV/AIDS pilot program that many clinical opportunities to make a diagnosis and offer treatment were being missed,” said Dr. Perry Kendall, provincial health officer of British Columbia, in a press release. “Based on this experience, we developed and released guidelines for front-line practitioners, recommending routine HIV screening for adults. This combination of increased testing and access to free antiretroviral drugs is both evidence-based and effective.”

The STOP HIV/AIDS pilot program was developed to specifically target at-risk individuals, as well as those who might already be infected, within Vancouver and the northern interior of British Columbia. By offering routine testing to over 24,000 people — with a full-fledged program currently offered, at-risk individuals aged 18 to 70 are recommended to get tested every year — and providing those who come up positive with free antiretroviral drugs, the researchers were able to reduce HIV rates within the first couple of years of the program. New cases of HIV dropped from 900 a year in the mid-1990s to 289 in 2011.

The researchers, from the University of British Columbia and the BC Centre for Excellence in HIV/AIDS, learned in their new study that, had it not been for testing, doctors wouldn’t have caught the virus. These screening tests, called rapid diagnostic tests, look for the HIV protein p24 and antibodies that are trying to fight the virus. As these tests are developed, they become better each time at diagnosing HIV earlier, with the current tests detecting HIV in as little as 16 to 18 days after infection. Still, routine testing is necessary in order to catch a positive where there was once a false negative.

“A simple blood test in conjunction with clinical evaluation enables us to detect this disease early and provide life-saving treatment,” said Dr. Julio Montaner, director of the BC Centre for Excellence in HIV/AIDS, in the release. "We know routine HIV testing works, and our goal is to bring the success we have had in British Columbia in controlling HIV and AIDS to the rest of Canada and around the world."

Over a million people aged 13 and older live with HIV in the U.S. However, a little over 15 percent have not yet been diagnosed, according to the Centers for Disease Control and Prevention. With so many people unknowing of their disease, and another 50,000 being diagnosed every year, early screening and prevention is the only way to catch the disease before it’s too late.