What is the defining feature of H1N1? If you ask the World Health Organization and the US Centers for Disease Control and Prevention, they will tell you that fever is the defining feature of H1N1. Unfortunately, that may not be entirely accurate.
Medical Journal The Lancet published an article where physicians in Australia found that nearly 30% of patients admitted to Gold Coast Hospital with H1N1 infections were afebrile, or without fever. These were confirmed H1N1 cases.
Buttressing the article is Dr. Richard Wenzel’s experience in Mexico and Chile. Dr Wenzel is an infectious disease specialist at Virginia Commonwealth University. He visited hospitals in Mexico City in the spring when the virus first exploded onto the scene. He did the same in Chile in July, during that country’s outbreak.
In both places, Dr. Wenzel observed a pattern like that seen in Australia, where approximately a third of adult H1N1 patients were afebrile. "If the CDC doesn’t recognize flu without fever, we’re going to miss a huge number of cases," notes Dr. Wenzel.
The CDC does recognize flu without fever and it is inherent in their guidelines on on preventing the spread of H1N1 that they acknowledge that fever need not be present in those afflicted with H1N1. Their report states that "depending on the case series, the proportion of persons who have laboratory confirmed 2009 H1N1 infection and do not have fever can range from about 10 to 50 percent."
Where the CDC falls short is in the agency’s practical guidance. The no-fever-is-necessary-for-H1N1 warning isn’t reflected in it, including when to keep children home from school or when parents should stay home from work or avoid public crowds. In those cases, the CDC defines flu in part by having an elevated temperature – a fever.
Flu experts are not certain whether a significant number of sufferers are afflicted enough to spread the virus, despite not being feverish. Dr. Wenzel and the Australian researchers figure that the number is at 30 percent or higher, but a Canadian study last month in the Journal of the American Medical Association found that only 10 percent of patients in intensive care were afebrile. Some even challenge 10 percent as being too high.
One thing that is clear is that H1N1 is more complicated than the seasonal flu in many ways. For starters, it’s more likely to cause gastrointestinal (GI) symptoms such as nausea and vomiting. The Canadian study indicated that approximately half of the patients admitted to intensive care were suffering GI problems. While many of those patients had mainly respiratory illness, approximately 10 to 15 percent complained primarily of GI symptoms, rather than the traditional symptoms related to cough and runny nose.
It is safe to say that just because someone isn’t suffering from flu like symptoms and thus isn’t dealing with elevated temperatures, that does not eliminate the possibility of H1N1, particularly when the patient exhibits GI symptoms.