Approach to an Infected Febrile PatientCHAPTER 1

Obtaining a complete and thorough history is of paramount in the evaluation of a patient with febrile infectious disease. Two main factors which determine the relevance of history to the disease are exposure and host specific factors.

Knowledge about exposure to methicilin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE) or enteric organisms produce extended spectrum beta lactamases or carbapenemase and/or recent stay in hospital or nursing homes may alter the choice of empirical antibiotics.^1,2

Knowing whether the patient has any high-risk behavior like, unsafe sexual activities, intravenous drug use or occupational exposures like funeral service, abattoir, and laboratory workers or hobbies like avid gardening, traveling, can facilitate diagnosis.2

Consumption of raw or undercooked meat are associated with Shiga toxin-producing Escherichia coli (STEC) and Toxoplasma gondii; unpasteurized milk with Listeria monocytogens and Mycobacterium tuberculosis; raw seafoods with Vibrio cholerae, Norovirus, helminths, and protozoa; unpurified water with Leptospira, parasites, and E. coli.

Contact with pets, visit to zoos, or random encounters with animals must be enquired about. For example, dogs carry ticks which transmit various infectious disease like rocky mountain spotted fever, lyme disease, and ehrlichiosis. Cats are associated with Bartonella henselae, reptiles with Salmonella, rodents with leptospirosis, and rabbits with tularemia infections.

Both international and domestic travel must be enquired about to broaden the differential diagnoses. The patient must be asked about the type of activities he was involved during his stay, e.g., the types of food and sources of water consumed, fresh water swimming, animal exposures, and whether he had necessary immunization and prophylactic medicines like yellow fever vaccine and prophylactic antimalarials before visiting endemic areas.^1,2

The immune status of the patient is of prime importance when it comes to opportunistic infections. Defects due to an underlying disease [like malignancy, human immunodeficiency virus (HIV) infection, and malnutrition], a medication (chemotherapy, glucocorticoids, and monocolonal antibodies), a treatment modality, (total body irradiation, splenectomy, or a primary immunodeficiency (Walderström's macroglobulinemia, diGeorge syndrome, chronic granulomatous disease) must be considered.^1,2

A thorough physical examination is crucial in evaluating patients with an infectious disease. The following components have particular relevance to infectious febrile diseases.

Structured approach to patients with fever is represented in figure 1.3

Elevation in temperature is a hallmark of infection, a temperature of more than 38.2°C (101°F), although fever is very commonly associated with infections, it is also documented in other diseases. Fever with hypotension, tachycardia, tachypnea, altered mentation, and respiratory distress points towards poor prognosis.

Lymph node examination in various regions (e.g., popliteal, inguinal, epitrochlear, axillary, and multiple cervical regions) with notation of size, i.e., <1 cm), location, tenderness, consistency, matted or not, generalized or localized can help narrow the diagnosis.^1,2

Owing to the fact many infections have cutaneous manifestations, skin examination is of particular importance in evaluation of patients. Specific rashes are extremely helpful in narrowing the differential diagnosis (e.g., measles, varicella, and arthropod infections). In numerous instances, the hospitalized patients with fever of unknown fever was actually due to pressure ulcers or thrombophlebitis.

Close attention should be given to the rash, first it is critical to determine the type of lesions (i.e., macules, plaques, papules, nodules, wheals, vesicles, bullae, pustules, purpura, ecchymoses, ulcer, or eschar). Other pertinent features include their configuration (i.e., annular or target), the arrangement of their lesions, and their distribution (i.e., central or peripheral).²4

With the advent of new laboratory and imaging techniques, the world of medical is revolutionized, however, all of these tests should be viewed as adjuncts to the history and physical examination but not a replacement for them.

Total leukocyte count and differential count is a prima facie of infections, both leukocytosis and leukopenia are important. It is important to assess differential count because different microbes are associated with various leukocyte types, for example, bacteria with polymorphs, viruses with lymphocytes, and parasites with eosinophils.

The erythrocytes sedimentation rate and C-reactive protein (CRP) are indirect and direct measures of the acute phase reactants, respectively, that can be used to monitor the status of the patient. It is noteworthy that weekly measurement of erythrocytes sedimentation rate (ESR) and daily of CRP is useful in the appropriate context. Although these are sensitive markers of inflammation none is specific.

Culture of the infected tissue sample (surgical specimens) or fluid (blood, urine, sputum, and purulence) from a wound is the mainstay of diagnosis. Culture allows identification of the organism and sensitivity to determine the susceptibility of the agent to antimicrobial.

Assessment of CSF is of utmost importance in patients suspected of meningitis or encephalitis. In general, CSF with a lymphocytic pleocytosis and a low glucose concentration suggests infection (with Listeria monocytogenes, Mycobacterium tuberculosis, or a fungus). Antigen testing (for Cryptococcus, Treponema pallidum, Coccidioides) is highly sensitive.5

Polymerase chain reaction is being increasingly used for the diagnosis of bacteria, e.g., Neisseria meningitidis, Streptococcus pneumonia, and Mycobacteria; and viruses (Herpes simplex and enteroviruses).^1,2

Imaging provides an important adjunct to the physical examination in evaluation of a patient of febrile infection, allowing evaluation of lymphadenopathy in regions not accessible externally (e.g., mediastinum, intra-abdominal sites), assessment of internal organs for evidence of infection, and facilitation of image guided percutaneous sampling.6

The modalities are X-ray, ultrasonography, computed tomography scan, magnetic resonance imaging, nuclear medicine, and contrasts imaging.^1,2

It is best to obtain relevant samples for culture prior to the administration of antibiotics. Broad empirical regimens are necessary to initiate, these regimens should be narrowed as appropriate specific diagnosis is made. In addition to antibiotics, sometimes there is role of adjunctive therapies, such as intravenous immunoglobulin G (e.g., Cytomegalovirus, hepatitis B, rabies, Vaccinia virus, Clostridium tetani, and botulinum toxin) or glucocorticoids as in tuberculosis meningitis.^1,2

Control of infectious disease is as important as diagnosing it to prevent further transmission of the organism.

The study of infectious disease is a study of interaction between host and the microbes and represents the evolution by both the host and the microbes, in which the microbes are at upper hand. So, in order to win the race and overcome the infections, the clinicians should use all their resources for early diagnosis and treatment of the cause. Finally, a precise and detailed history and a thorough physical examination amalgamated with the laboratory studies will clinch the diagnosis.