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Information for Health Care Providers

Distinguishing Between Influenza-like Illness
and Early Inhalation Anthrax

In most circumstances, the Illinois Department of Public Health does not make specific recommendations about patient care. However, it is providing the following information, which may help with clinical decisions. Ultimately, though, clinical decisions about patient care remain with the health care provider.

It is important that health care providers follow reporting requirements. When a diagnosis of a bioterrorism-associated illness is suspected, it is critical that the case be reported to the local health department within three hours of such recognition.

1. Health care providers should review the Morbidity and Mortality Weekly Report (November 2, 2001).

Of particular importance is the flow diagram on page 945 (Figure 2, reproduced below). Additional guidance from the U.S. Centers for Disease Control and Prevention (CDC) can be found in the November 9, 200, issue (Vol. 50, No. 44) of the MMWR. Another article of interest will appear in the November 29, 2001, issue of the New England Journal of Medicine: “Recognition and management of anthrax - an update” by M.N. Swartz.

figure 2

2. Anthrax is rare and influenza-like illnesses are common.

Although the symptoms of influenza and influenza-like illnesses may overlap with the early presentation of inhalation anthrax, it should be emphasized that influenza is primarily an upper respiratory tract infection (e.g., cough and sore throat) with accompanying fever, headache, myalgia and malaise but with a wide spectrum of severity. Recently reported cases of inhalation anthrax , a lower respiratory tract infection, may have minimal or nonproductive cough but frequently have chest discomfort or pleuritic pain. When influenza is complicated by lower respiratory tract findings, such as pneumonia, then differentiating from anthrax may be more difficult. Whenever inhalation (or any form of) anthrax is being considered, consultation with an infectious disease physician is recommended.

Based on review of the relatively few published cases of inhalation anthrax and the recent bioterrorism-related cases, rhinitis is rarely, if ever, seen with anthrax. Its presence, therefore, is a possible clue that influenza or influenza-like illness is present; however, its absence is of no value because many cases of influenza and influenza-like illnesses will not have rhinitis.

Symptoms such as fever, sweats, chills, myalgias, fatigue, malaise, dry cough, headache and sore throat may occur in either illness, so their presence or absence is of no value. But the rarity of anthrax and the relative frequency of influenza and influenza-like illnesses should be considered when doing a diagnostic evaluation, just as the incidence of illnesses guides other decisions in clinical medicine. Clinicians should avoid letting fear obscure sound clinical judgment.

There are no early laboratory clues that can be considered diagnostic. It has been noted that none of the inhalation anthrax cases had a low white blood cell count. This information cannot be reliably used to differentiate anthrax from other illnesses since it is possible that anthrax could infect someone who already has a low white blood cell count (e.g., an immunocompromised person). Also, the number of studied anthrax cases is still relatively small, so generalizations about the disease are limited.

3. Occupation and exposure history should be obtained to help assess the relative risk of anthrax in an individual presenting with influenza-like illness.

To date, nearly all cases of inhalation anthrax have been either a postal worker, a mail handler or sorter, or a recipient of an envelope containing anthrax spores. For a few additional cases, the exposure has not been determined but those investigations are ongoing. Therefore, risk is certainly increased if someone is linked to one of the confirmed anthrax events in the District of Columbia, Florida, New Jersey or New York City. And, heightened concern is reasonable if dealing with persons who handle mail or who have been exposed through an incident that appears to be credible or that was determined by law enforcement to be credible and for which laboratory evidence has not ruled out anthrax.

4. Rapid influenza tests may be performed to help evaluate a case of anthrax versus influenza.

Such testing has limitations that do not make it reliable for this purpose. While makers of the rapid influenza tests report overall sensitivity of 70 percent and specificity of 90 percent, these are likely overestimates based on unpublished data of which the CDC is aware. In fact, it is not unusual for rapid influenza tests to yield false positives and false negatives. During peak flu season, only one-third of influenza-like illnesses submitted for viral testing actually test positive for influenza. The positive predictive value of these tests suffer during non-peak portions of the flu season. So, a negative rapid influenza test does not mean a person has anthrax.

5. To date, there have been no cases of anthrax nor environmental test results positive for anthrax in Illinois.

Millions of cases of influenza-like illness occur every year. Therefore, while public health officials and health care providers need to be in a state of heightened awareness for anthrax, it is important to keep in mind that, for any individual case, the odds are very small that it is truly anthrax.

6. If diagnostics are performed to evaluate a possible human case of anthrax, such specimens should be initially processed in a local hospital or other qualified laboratory, unless such testing requires specialty techniques such as PCR or immunohistochemical testing of tissue.

If test results suggest the presence of a Bacillus species that may be B. anthracis, then the local health department should be notified immediately so that staff can consult with IDPH laboratory personnel or the Department’s infectious disease staff about forwarding such specimens to the state laboratory for confirmation or speciation.

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Illinois Department of Public Health
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Springfield, Illinois 62761
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TTY 800-547-0466
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