Clinical Features

Symptoms of SEB intoxication begin after 3-12 hours after inhalation, or 4-10 hours after ingestion. Symptoms include nonspecific flu-like symptoms (fever, chills, headache, muscle aches).

Oral exposure results in predominantly gastrointestinal symptoms: nausea, vomiting, and diarrhea. Inhalation exposures produce predominantly respiratory symptoms: nonproductive cough, chest pain, and shortness of breath. GI symptoms may accompany respiratory exposure due to inadvertent swallowing of the toxin after normal postnasal drip.

Respiratory illness is due to the activation of pro-inflammatory cytokine in the lungs, leading to pulmonary capillary leak and pulmonary edema. Severe cases may result in acute pulmonary edema and respiratory failure.

The fever may last up to five days and range from 103° to 106°F, with variable degrees of chills and prostration. The cough may persist up to four weeks. Physical examination of casualties shows no easily discernible traits. Symptoms may develop as conjunctivitis and/or low blood pressure due to fluid losses. Chest examination is unremarkable except in the unusual case where pulmonary edema develops. A chest X-ray is also generally normal, but in severe cases increased interstitial markings, partial collapse of a lung, and possibly overt pulmonary edema may appear.

Mechanism of Toxicity

Staphylococcal enterotoxins belong to a class of potent immune stimulants known as bacterial superantigens. This leads to the direct stimulation of large populations of T-helper cells while bypassing the usual antigen mechanisms. This results in an intense inflammatory response that injures host tissues. Cytokines released by cells of the immune system are thought to mediate many of the toxic effects of SEB.

Diagnosis

Diagnosis of SEB intoxication is based on medical evaluation and epidemiologic reports. Because the symptoms of SEB intoxication may be similar to several respiratory illnesses such as influenza or pleuropneumonia, the diagnosis may initially be unclear. Symptoms include fever, dry cough, muscle aches, and headache. An SEB attack would cause large numbers of cases over a very short period of time, probably within a single 24-hour period.

Naturally occurring pneumonias or influenza would involve casualties presenting over a more prolonged interval of time. Naturally occurring staphylococcal food poisoning cases do not have pulmonary symptoms. SEB intoxication tends to plateau rapidly to a fairly stable clinical state, whereas inhalational anthrax, tularemia pneumonia, or pneumonic plague would all continue to progress if left untreated. Tularemia and plague, as well as Q fever, would be seen on chest X-rays. Other diseases, including Hantavirus pulmonary syndrome, chlamydia pneumonia, and chemical warfare agent inhalation (mustard, phosgene), should also be considered.

Medical Management

Therapy is limited to supportive care. Close attention to oxygenation and hydration is important, and in severe cases with pulmonary edema, ventilation with positive end expiratory pressure, vasopressors, and diuretics might be necessary. Acetaminophen for fever, and cough suppressants may make the patient more comfortable. Most casualties would be expected to do quite well after the initial acute phase of their illness, but generally would require one to two weeks to recover. Severe cases may lead to death from pulmonary edema and respiratory failure.

Preventative Measures

Although there is currently no human vaccine for immunization against SEB intoxication, several test vaccines are under development. Experimentally, passive immunotherapy can reduce mortality in animals, but only when given within 4-8 hours after inhaling SEB. Most people have detectable antibodies to SEB and SEC1; however, immunity acquired through natural exposure to SEB does not provide complete protection from an aerosol exposure (although it may reduce nausea).