Prehospital Clinical Diagnosis by EMS personnel does not require a thermometer to recognize an infectious disease. Many other signs and symptoms can lead to the diagnosis of fever and associated infectious disease: chills, rigors, sweats, altered mental status, or patient's history of fever or associated symptoms. Concerning symptoms specific to the infected body system (a cough in a lung infection, a rash in a skin infection, abdominal pain in diverticulitis, etc. ) should lead the EMS provider to suspect infection and include it on the differential diagnosis. High suspicion of an infectious disease can improve patient treatment as well as protect the providers from possible infectious exposures. Although universal precautions should be taken with all patients, significantly better protocol adherence is achieved when EMS personnel have a high suspicion of infectious disease. Proper assessment of patient history, presentation, and physical exam can add to the appropriate suspicion of infectious disease.
Baseline vital signs in EMS certainly include pulse, respirations, skin color, skin temperature and skin condition, and blood pressure. These vital signs comprise an important part of the physical assessment in EMS. It may also be argued that these vital signs should include skin temperature to touch (or with a thermometer if available). Does the skin feel cool/normal or warm/hot to the touch? The clinical evaluation of tactile temperature has been shown to be at least as accurate as topical (e.g., temporal) thermometry, even in untrained personnel (e.g., mother's of sick children, etc.). Certainly, trained EMS personnel will use this technique, as part of their careful clinical assessment when evaluating a possible infectious disease. Many other historical clues and physical findings may aid the EMS provider.
The subjective assessment of fever, as well as the assessment of other signs and symptoms that occur with infectious disease, is important in EMS. Pulse can be high due to fever, or with possible associated dehydration or shock. Palpating a pulse not only gives an accurate rate, but it also gives information about the effectiveness of blood pressure and flow. This can be of significant concern with a severe infectious disease, especially sepsis. Shock can develop quickly and differentiating infectious cause for shock will be important for definitive treatment. Unfortunately, people taking medications affecting the heart rate (such as beta blockers or calcium channel blockers) may not mount a tachycardic response, so a normal heart rate does not rule out fever or infection. Additionally, sepsis, especially in the elderly, can actually cause bradycardia (associated with end-organ failure.)
Respiratory rate also may be elevated as a direct response to fever. Studies have suggested that respiratory rate can increase up to 5 bpm for each degree Fahrenheit elevation of core body temperature. Although tachypnea forces additional assessment looking for respiratory distress, hypoxia, or ineffective ventilation, it can also be a direct result of fever and infection. Recognition of this correlation may improve infectious treatment and potentially avoid unneeded intervention, both prehospital and in the hospital setting.
Skin color, skin temperature, and skin condition may give a surprising amount of information. Red, flushed faces are familiar to every parent with a febrile child. Generalized, or especially central (face and torso), skin erythema occurs as a result of vascular dilation. This vasodilation is part of a feedback mechanism to fever, allowing the patient to decrease heat retention. Tactile temperature (Does the patient feels warm/hot to touch?) is surprisingly accurate in studies. The parents' or patient's history, or the EMS personnel assessment, of "hot to touch" needs to be noted and conveyed to the accepting medical providers. Additionally, the condition of the skin, including diaphoresis and redness/erythema, may aid in the diagnosis of an infectious disease. Diaphoresis and skin erythema may increase as a fever improves, though, as these are mechanisms to decrease retained heat in the body. Rashes of many types can be associated with infectious disease; however, of special concern are petechiae or purpura which can be associated with vascular and platelet malfunction or sepsis and generalized exanthems, which can be associated with or be diagnostic of specific infectious disease (such as measles, chicken pox, etc). Decreased capillary refill may be due to poor hydration or due to peripheral vasoconstriction. Peripheral cyanosis may also occur, especially in very young patients, from vasoconstriction. This peripheral vasoconstriction, which can prolong capillary refill and increase cyanosis, actually helps the patient by shunting blood away from the arms and legs to increase the blood flow to the more important central organs (brain, heart, lungs, kidneys, etc.).
Blood pressure is also of critical importance in the assessment of infectious disease. Vascular dilation associated with fever can decrease blood pressure, causing decreased blood flow to critical organs. This is especially true if exacerbated by dehydration or cardiac compromise, including medications. If hypotensive, central nervous system effects of the infectious disease will increase in addition to decreased urine output, gastrointestinal dysfunction, and cyanosis. This is part of the spectrum of sepsis and septic shock and can signify a critical finding that needs immediate treatment.
Additional signs may also point to infectious disease and can be assessed without special tools. Although not specific to fever or infectious disease, chills, shivering, "goose bumps"/piloerection, and altered mental status are all important indicators that should increase the provider's suspicion of infectious disease. 
Safe EMS practices will assume the possibility of infectious disease in a person with symptoms, history, or physician assessment signs which suggest infection. Proper protection of the patient (and EMS personnel) and properly communicating this clinical diagnosis to receiving facility is required for good prehospital care. Although thermometers are now often available for EMS personnel, clinical assessment is an even more important consideration in the assessment of infectious disease.
Evaluation of the patient's vital signs, including pulse, respirations, and blood pressure, should accompany a focused physical assessment. Tactile skin temperature, color, and condition also can give important information. Altered mental status, decreased cardiac function, and evidence of any end organ failure should increase concern over serious infectious disease or sepsis. The patient's history of symptoms, clinical course, and exposures may aid the final diagnosis, also.