Diverticulitis: This condition is common in older adults and can cause lower abdominal cramping, changes in bowel habits including loose stools mixed with mucous and blood, without necessarily presenting with fever or chills in its early stages. The absence of fever does not rule out diverticulitis, especially if the patient is taking anti-inflammatory drugs or if the condition is mild.

Irritable Bowel Syndrome (IBS): Although IBS typically does not cause bloody stools, some variants can present with mixed bowel habits and abdominal pain. The presence of mucous and some blood might suggest an inflammatory component, but IBS should be considered, especially if other symptoms like bloating and changes in stool frequency are present.
Inflammatory Bowel Disease (IBD): Conditions like ulcerative colitis or Crohn's disease can cause chronic diarrhea, abdominal pain, and blood in the stool. The absence of fever and chills does not rule out IBD, as these symptoms can wax and wane.
Gastroenteritis: Although the patient denies fever and chills, a viral or bacterial gastroenteritis could still be a consideration, especially if the onset was sudden. Some pathogens might cause a more insidious onset of symptoms without systemic signs of infection.

Colorectal Cancer: This is a critical diagnosis not to miss, as it can present with changes in bowel habits, including diarrhea or constipation, and blood in the stool. The presence of mucous could be indicative of a tumor. Age is a significant risk factor, making this a diagnosis that must be ruled out.
Infectious Colitis: Certain bacterial infections (e.g., Clostridioides difficile, Salmonella, Shigella) can cause severe diarrhea, abdominal cramping, and blood in the stool. While the patient does not have fever or chills, these symptoms can be absent in some cases, especially in older adults or those with compromised immune systems.
Ischemic Colitis: This condition occurs when there is insufficient blood flow to the colon and can present with sudden onset of abdominal pain and bloody diarrhea. It is more common in older adults and those with vascular disease.

Microscopic Colitis: This condition can cause chronic watery diarrhea and abdominal pain but typically does not cause bloody stools. However, it's a consideration in patients with chronic symptoms that do not fit into other categories.
Lymphocytic Colitis: Similar to microscopic colitis, it presents with chronic diarrhea but is less likely to cause bloody stools. It's a rare condition but should be considered in the differential diagnosis of chronic diarrhea.
Eosinophilic Colitis: A rare condition characterized by eosinophilic infiltration of the colonic mucosa, which can cause abdominal pain, diarrhea, and sometimes blood in the stool. It's more common in patients with a history of atopy or eosinophilic esophagitis.