[1] He completed his residency in internal medicine and infectious diseases at Harvard Medical Service at Boston City Hospital, where Maxwell Finland was his supervising attending physician and mentor.
In field studies, particularly in Brazil, he and his colleagues investigated the developmental problems of children who suffered from persistent diarrheal diseases in the critical first years of their lives.
Guerrant and his team also found that APOE-ε4, the main risk allele in Alzheimer's disease, protects children against such cognitive losses due to diarrhea.
[2] The Infectious Diseases Society of America honored Guerrant with the Joseph E. Lectureship in 1993[9] and the Walter E. Stamm Mentor Award in 2009.
[14] He received in 2008 the Walter Reed Medal from the ASTMH[15] and in 2014 the Maxwell Finland Award from the National Foundation for Infectious Diseases.