# 3174
The H1N1 virus is quite new, and doctors and scientists are just starting to learn about how it affects humans.
Thus far, there appear to be major differences between the symptoms and outcomes in Mexico, and those seen in the United States and Europe.
Right now, the reasons for that are far from clear.
Today, we’ve a fascinating report from a doctor who spent several days in Mexico treating H1N1 patients, and he reports that as many as 1/3rd of the cases hospitalized presented without a fever.
Given that fever is almost universally accepted as an early sign of a viral illness, and that almost all screening for influenza looks first for an elevated temperature, a lack of a fever in up to 1/3rd of cases creates real problems in making a diagnosis.
First this report (which you should read in its entirety) from the New York Times, then some discussion.
Many Swine Flu Cases Have No Fever
By LAWRENCE K. ALTMAN
Published: May 12, 2009
Many people suffering from swine influenza, even those who are severely ill, do not have fever, an odd feature of the new virus that could increase the difficulty of controlling the epidemic, said a leading American infectious disease expert who examined cases in Mexico last week.
Fever is a hallmark of influenza, often rising abruptly to 104 degrees at the onset of illness. Because many infectious disease experts consider fever the most important sign of the disease, the presence of fever is a critical part of screening patients in an influenza outbreak.
But about a third of the patients at two hospitals in Mexico City where the American expert, Dr. Richard P. Wenzel, consulted for four days last week had no fever when screened, he said.
“It surprised me and my Mexican colleagues because the textbooks say that in an influenza outbreak the predictive value of fever and cough is 90 percent,” Dr. Wenzel said by telephone from Virginia Commonwealth University in Richmond, where he is chairman of the department of internal medicine.
While many people with severe cases went on to develop fever after they were admitted, about half of milder cases did not; nearly all patients had coughing and malaise, Dr. Wenzel said.
Here in the United States, an early analysis of over 600 confirmed H1N1 cases from 41 states produced these demographics, and symptoms:
- 104 cases were from four clusters in schools or universities.
- The age range of patients was 3 months to 81 years
- 40% were between ages 10 and 18 years,
- Only 5% were older than 50.
- Of the 381 patients with complete data, 68 (18%) had recently traveled to Mexico.
- Predominant symptoms were fever (94%), cough (92%), and sore throat (66%).
- Vomiting and diarrhea were less common (25%).
It is possible, I suppose, that since the suspect case definition here in the US is biased towards patients presenting with a fever - that might exclude non-febrile cases from testing - which would skew the above numbers a bit.
Or perhaps we really are seeing a different presentation here in the United States and Canada.
One doctor’s anecdotal report, while compelling, isn’t conclusive. But it does beg further examination and research.
Right now there are far more questions than answers surrounding this novel virus.
Each day seems to bring new surprises.
Stay tuned.
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