Many Swine Flu Cases Have No Fever

[indigo girl]

http://www.nytimes.com/2009/05/13/health/13fever.html?_r=3&partner=rss&emc=rss

This is important information about the clinical presentation of this disease with implications for testing, and controlling the disease.

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.

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.

While many people with severe cases went on to develop fever after they were admitted, about half of the milder cases did not; nearly all patients had coughing and malaise, Dr. Wenzel said.

Also, about 12 percent of patients at the two Mexican hospitals had severe diarrhea in addition to respiratory symptoms like coughing and breathing difficulty, said Dr. Wenzel, who is also a former president of the International Society for Infectious Diseases. He said many such patients had six bowel movements a day for three days.

Dr. Wenzel said he had urged his Mexican colleagues to test the stools for the presence of the swine virus, named A(H1N1). "If the A(H1N1) virus goes from person to person and there is virus in the stool, infection control will be much more difficult," particularly if it spreads in poor countries, he said.

The doctor said he had also urged his Mexican colleagues to perform tests to determine whether some people without symptoms still carried the virus.

[P_RN, ADN, RN]

I don't believe I run a fever. The other month with presumed pneumonia i ahd all the other sx but no fever. High is usually 98-99F

[indigo girl]

H1N1 Influenza Center at NEJM

This is a new site with several studies of interest on S-OIV. We seem to be moving away from calling it Swine Flu or Type A, H1N1.

http://h1n1.nejm.org/

Emergence of a Novel Swine-Origin Influenza A (H1N1) Virus in Humans

http://content.nejm.org/cgi/content/full/NEJMoa0903810

In the United States to date, most confirmed cases of S-OIV infection have been characterized by self-limited, uncomplicated febrile respiratory illness and symptoms similar to those of seasonal influenza (cough, sore throat, rhinorrhea, headache, and myalgia), but approximately 38% of cases have also involved vomiting or diarrhea, neither of which is typical of seasonal influenza. However, some patients have been hospitalized with more severe disease, and two patients have died. The observation that 60% of patients were 18 years of age or younger suggests that children and young adults may be more susceptible to S-OIV infection than are older persons or that because of differences in social networks, transmission to older persons has been delayed. It is also possible that elderly persons may have some level of cross-protection from preexisting antibodies against S-OIV infection, as suggested by serologic studies of the 1976 swine influenza vaccine.5,6 A potential case-ascertainment bias may also exist, with more young people being tested as part of outbreaks of S-OIV infection in schools7 and fewer older persons being tested for influenza. However, the epidemic is evolving rapidly, and the number of confirmed cases is an underestimate of the number of cases that have occurred.

Continued identification of new cases in the United States and elsewhere indicates sustained human-to-human transmission of this novel influenza A virus. The modes of transmission of influenza viruses in humans, including S-OIV, are not known but are thought to occur mainly through the dissemination of large droplets and possibly small-particle droplet nuclei8 expelled when an infected person coughs. There is also potential for transmission through contact with fomites that are contaminated with respiratory or gastrointestinal material.9,10 Since many patients with S-OIV infection have had diarrhea, the potential for fecal viral shedding and subsequent fecal-oral transmission should be considered and investigated. Until further data are available, all potential routes of transmission and sources of viral shedding should be considered.

The incubation period for S-OIV infection appears to range from 2 to 7 days; however, additional information is needed. On the basis of data regarding viral shedding from studies of seasonal influenza, most patients with S-OIV infection might shed virus from 1 day before the onset of symptoms through 5 to 7 days after the onset of symptoms or until symptoms resolve; in young children and in immunocompromised or severely ill patients, the infectious period might be longer.11 Studies of viral shedding to define the infectious period are under way. The potential for persons with asymptomatic infection to be the source of infection to others is unknown but should be investigated.

The clinical spectrum of novel S-OIV infection is still being defined, but both self-limited illness and severe outcomes, including respiratory failure and death, have been observed among identified patients-a wide clinical spectrum similar to that seen among persons infected with earlier strains of swine-origin influenza viruses3 and seasonal influenza viruses.12 The severe illness and deaths associated with seasonal influenza epidemics are in large part the result of secondary complications, including primary viral pneumonia, secondary bacterial pneumonia (particularly with group A streptococcus, Staphylococcus aureus, and Streptococcus pneumoniae),13,14,15 and exacerbations of underlying chronic conditions.16 These same complications may occur with S-OIV infection. Patients who are at highest risk for severe complications of S-OIV infection are likely to include but may not be limited to groups at highest risk for severe seasonal influenza: children under the age of 5 years, adults 65 years of age or older, children and adults of any age with underlying chronic medical conditions, and pregnant women[.17,18 Of the 22 hospitalized patients with confirmed S-OIV infection who have been identified thus far and for whom data are available, 12 had characteristics (pregnancy, chronic medical conditions, or an age of less than 5 years) that conferred an increased risk of severe seasonal influenza, although none of the patients were 65 years of age or older.

(hat tip flutrackers/The Doctor)

[indigo girl]

Swine flu: is there something unusual about the symptoms?

I don't believe I run a fever. The other month with presumed pneumonia i ahd all the other sx but no fever. High is usually 98-99F

Apparently the absence of fever is not that unusual and you can be very sick despite that. And, mild cases with no fever will not be tested, but then can spread the virus to others.

http://scienceblogs.com/effectmeasure/2009/05/swine_flu_is_there_something_u.php

...the absence of fever might not be particularly unusual. On the other hand, the relatively high prevalence of gastrointestinal symptoms is a worry:

Also, about 12 percent of patients at the two Mexican hospitals had severe diarrhea in addition to respiratory symptoms like coughing and breathing difficulty, said Dr. Wenzel, who is also a former president of the International Society for Infectious Diseases. He said many such patients had six bowel movements a day for three days.

Dr. Wenzel said he had urged his Mexican colleagues to test the stools for the presence of the swine virus, named A(H1N1). "If the A(H1N1) virus goes from person to person and there is virus in the stool, infection control will be much more difficult," particularly if it spreads in poor countries, he said. (NYT)

Gastrointestinal symptoms are also seen in H5N1 patients. The question whether there is intestinal infection and carriage is of importance. We know little about the distribution of appropriate viral receptors in tissues outside the respiratory tract, and some data suggests that flu virus can successfully make the passage through the acid environment of the upper g.i. tract. Is ingestion a possible route for influenza infection? Conventional wisdom says, "no."

But influenza is the surprise that keeps surprising.

One of the perks of reading the Reveres at Effect Measure is that there are some very interesting comments from clinicians working with these patients, lab scientists etc. Check out comment #22 from someone who self describes as an ER doc. Not only does he describe patients with no fever, but also points out that initial swabs can be negative but turn out to be positive later.

The Reveres have said before that these tests are known to miss about 50% of the true positives.

Perspective from the ER:

I have been involved with the care of several individuals with confirmed Influenza A/H1N1 2009 N. America (SO-IV) What has amazed me is that 1 of the cases had no fever and no symptoms--yet had an initial rapid Flu swab that was positive and sub-typed several days later to confirm SO-IV. Of note this person had done some air travel--so much for screening--lets stop that draconian nonsense and spend the money on more useful things like vector surveillance. The other 2 had fever--but only very mild --and barely reaching the case definition temp. In addition, one of the low grade fever cases had a negative initial rapid flu swabs but positive PCR that came back the next day and then confirmed SO-IV of the swab. . This translates into a PITA from an Emergency Medicine triage perspective since we typically think of influenza as the sudden onset of a train hitting you with fever and rigors. This puppy likes to elude. Confucius say :no or low fever with poor reliable rapid flu makes major headache for world.

Posted by: BostonERDoc | May 14, 2009 9:56 PM

[Katnip, RN]

What makes me wonder about this, is how many people contracted this flu but thought they were having a few days to a week of really bad allergy symptoms that resolved on their own.

I had a total of 7 days of miserable allergy problems with a very low grade fever for part of the time. Then suddenly the worst symptoms were gone. I saw an allergist at the tail end when I was starting to feel better and got meds and felt totally better.

I do have seasonal allergies but have never had them this bad before, but it's said to be an extremely bad season.

Lots of people at work had the cough, sore throat, etc. but no fever. None of us thought to get tested because the guidelines all said the fever would be 37.9 or greater.

So maybe this thing is far more widespread than we see?

[indigo girl]

So maybe this thing is far more widespread than we see?

I think so too. The true extent may never be known.

I am getting more concerned about reports of severe cases with no pre-existing conditions or conditions that should not influence the severity of an influenza infection. It's starting to get rather annoying in fact.

[lamazeteacher]

I think so too. The true extent may never be known.

I am getting more concerned about reports of severe cases with no pre-existing conditions or conditions that should not influence the severity of an influenza infection. It's starting to get rather annoying in fact.

I've brought up the possibility of having home testing for H1N1. There is a specific time during which patients with this novel flu will have a positive result, and it's after the 3rd or 4th day. Yet Tamiflu needs to be started during the first 48 hours of it. I haven't read anything yet that says Tamiflu can render the test negative.....

A side benefit of this is the inclusion of patients as a member of their health care team. Certainly those with GI bleeding episodes are entrusted with the far more difficult task of attaining stool for occult blood testing (the specimen can't hit the water in the toilet).

I have contacted CDC and WHO in this regard, but you know how long it can take, for big agencies to get going on anything........... There could be a very short questionnaire included in the kit, to see if s/s are appropriate for testing. Direct involvement of the patient reduces communication errors, by taking out the middle person (doctor or MA).