of identifying a parasite may be increased by examining additional stool samples (three samples obtained on separate occasions increase the sensitivity to more than 90%) Management: In many cases of persistent diarrhea, no causative agent can be identified In these cases, some experts recommend empiric antimicrobial therapy such as a macrolide for suspected bacterial enteritis Metronidazole (or a related agent such as nitazoxanide) is recommended for presumed giardiasis, since G lamblia is the most commonly identified intestinal parasite in travelers Multiple courses of antimicrobial agents should be avoided For travelers whose diarrhea persists, endoscopic examination and biopsy should be considered to exclude entities such as tropical sprue and inflammatory bowel disease Contact precautions are recommended SYSTEMIC INFECTIONS IN THE RETURNED TRAVELER There are several treatable infections that may affect travelers who have systemic manifestations, including hemorrhage These include meningococcemia, malaria, leptospirosis, and rickettsial infections There are a handful of viral infections (in addition to dengue and yellow fever) that are also associated with fever and hemorrhage; these, however, are rarely acquired by travelers Viral hemorrhagic fevers (such as Lassa fever and Ebola fever) need to be considered in travelers who present with fever and hemorrhage; these diseases also have important infection control and public health concerns Epidemiologic clues include history of visits to rural areas or recent contact with ill persons in areas where the viral hemorrhagic fevers are endemic Most patients with viral hemorrhagic fevers note the onset of fever within weeks after exposure to infected persons, contaminated water, or infected insects/vectors There is currently no specific treatment available for the viral hemorrhagic fevers Supportive care with special attention to careful fluid and electrolyte management is indicated Endothelial dysfunction makes hydration challenging; pulmonary edema occurs rapidly with intravenous hydration To prevent agitation, analgesia and sedation may be useful Yellow Fever Yellow fever is a tropical zoonotic infection caused by a flavivirus transmitted from nonhuman primates to humans by mosquitoes of the Aedes (in Africa) and Haemagogus (in Latin America) genera Following a 3- to 6-day incubation period, patients develop an influenza-like illness with fever, chills, headache, photophobia, back pain, and myalgias lasting approximately days, followed by spontaneous resolution in almost 80% of patients The remaining 15% to 20% of patients then develop fever, abdominal pain, vomiting, and jaundice Oliguria and hemorrhagic findings can be seen Laboratory findings include leukopenia, thrombocytopenia, transaminitis, disseminated intravascular coagulation, and proteinuria Most patients experience remission of symptoms after an initial 3- to 4-day period Patients who continue to have symptoms or develop biphasic illness can progress to multiorgan system dysfunction; in these cases, mortality rates range from 20% to 50% Treatment is supportive, often in an intensive care unit setting A live-attenuated vaccine is available for children older than to months and is required for entry into some Latin American and sub-Saharan African nations Insecticide-impregnated bed nets not prevent yellow fever, as the mosquito vectors are daytime feeders Standard precautions are recommended Leptospirosis Leptospirosis is caused by Leptospira interrogans, a spirochete transmitted in the urine or placental tissue of rodents and other infected nonhuman animals As organisms can remain viable under moist conditions (soil or water) for months, the infection can also be spread via contact with bodies of water or after persons have been in regions where flooding has occurred Humans become infected via entry of leptospires through mucosal surfaces or skin abrasions While it has a global distribution, it is more common in tropical and subtropical regions Most cases are mild or asymptomatic Severe cases typically are bimodal, with an initial septicemic phase and a second immune phase The septicemic phase can be icteric (Weil syndrome) or anicteric and is characterized by an influenza-like illness lasting less than week Following this, a subset of patients will develop headache, nuchal rigidity, rash (sometimes petechial), hepatomegaly, and conjunctival suffusion Renal involvement may consist of pyuria, hematuria, proteinuria, or acute kidney injury The most severe form is Weil syndrome, characterized by icterus and hepatorenal syndrome; it carries a 5% to 10% mortality rate The diagnosis is based upon acute and convalescent serologies Parenteral penicillin is the treatment of choice Clinicians should be aware of Jarisch– Herxheimer reactions (acute febrile illness, myalgia, headache lasting less than day) after initiation of therapy as