Manifestations of infection may be local (eg, cellulitis, abscess) or systemic (most often fever Fever Fever is an elevated body temperature that occurs when the body's thermostat (located in the hypothalamus) resets at a higher temperature, primarily in response to an infection. Elevated body... read more ). Manifestations may develop in multiple organ systems. Severe, generalized infections may have life-threatening manifestations (eg, sepsis and septic shock Sepsis and Septic Shock Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection. In septic shock, there is critical reduction in tissue perfusion; acute failure... read more ). Most manifestations resolve with successful treatment of the underlying infection.
Clinical
Most infections increase the pulse rate and body temperature, but others (eg, typhoid fever, tularemia, brucellosis, dengue) may not elevate the pulse rate commensurate with the degree of fever (relative bradycardia). Hypotension can result from hypovolemia, septic shock, or toxic shock Toxic Shock Syndrome (TSS) Toxic shock syndrome is caused by staphylococcal or streptococcal exotoxins. Manifestations include high fever, hypotension, diffuse erythematous rash, and multiple organ dysfunction, which... read more 
. Hyperventilation and respiratory alkalosis are common.
Alterations in sensorium (encephalopathy) may occur in severe infection regardless of whether central nervous system infection is present. Encephalopathy is most common and serious in older adults and may cause anxiety, confusion, delirium, stupor, seizures, and coma.
Hematologic
Infectious diseases commonly increase the numbers of mature and immature circulating neutrophils. Mechanisms include demargination and release of immature granulocytes from bone marrow, interleukin-1– and interleukin-6–mediated release of neutrophils from bone marrow, and colony-stimulating factors elaborated by macrophages, lymphocytes, and other tissues. Exaggeration of these phenomena (eg, in trauma, inflammation, and similar stresses) can result in release of excessive numbers of immature leukocytes into the circulation (leukemoid reaction), with leukocyte counts up to 25,000 to 30,000/mcL (25 to 30 × 109/L).
Conversely, some infections (eg, typhoid fever, brucellosis) commonly cause leukopenia. In overwhelming, severe infections, profound leukopenia is often a poor prognostic sign.
Characteristic morphologic changes in the neutrophils of septic patients include Döhle bodies, toxic granulations, and vacuolization.
Anemia can develop despite adequate tissue iron stores. If anemia is chronic, it is a normochromic, normocytic anemia characterized by low serum iron, low total iron-binding capacity, and normal to increased serum ferritin.
Serious infection may cause thrombocytopenia Thrombocytopenia: Other Causes Platelet destruction can develop because of immunologic causes (viral infection, drugs, connective tissue or lymphoproliferative disorders, blood transfusions) or nonimmunologic causes (sepsis... read more and disseminated intravascular coagulation Disseminated Intravascular Coagulation (DIC) Disseminated intravascular coagulation (DIC) involves abnormal, excessive generation of thrombin and fibrin in the circulating blood. During the process, increased platelet aggregation and coagulation... read more (DIC).
Other organ systems
Pulmonary compliance may decrease, progressing to acute respiratory distress syndrome Acute Hypoxemic Respiratory Failure (AHRF, ARDS) Acute hypoxemic respiratory failure is defined as severe hypoxemia (PaO2 (See also Overview of Mechanical Ventilation.) Airspace filling in acute hypoxemic respiratory failure (AHRF) may result... read more 
(ARDS) and respiratory muscle failure.
Renal manifestations range from minimal proteinuria to acute renal failure Acute Kidney Injury (AKI) Acute kidney injury is a rapid decrease in renal function over days to weeks, causing an accumulation of nitrogenous products in the blood (azotemia) with or without reduction in amount of urine... read more , which can result from shock and acute tubular necrosis, glomerulonephritis, or tubulointerstitial disease.
Hepatic dysfunction, including cholestatic jaundice (often a poor prognostic sign) or hepatocellular dysfunction, occurs with many infections, even though the infection does not localize to the liver.
Gastrointestinal (GI) manifestations include upper GI bleeding due to stress ulceration that may occur during sepsis.
Endocrinologic dysfunctions include
Increased production of thyroid-stimulating hormone, vasopressin, insulin, and glucagon
Breakdown of skeletal muscle proteins and muscle wasting secondary to increased metabolic demands
Bone demineralization
Hypoglycemia Hypoglycemia Hypoglycemia, or low plasma glucose level can result in sympathetic nervous system stimulation, and central nervous system dysfunction. In patients with diabetes who take insulin or antihyperglycemic... read more occurs infrequently in sepsis, but adrenal insufficiency should be considered in patients with hypoglycemia and sepsis. Hyperglycemia Diabetes Mellitus (DM) Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia... read more may be an early sign of infection in diabetics.
