Differential Diagnosis for Unexplained Chills and Mild URI Symptoms without Fever

Single Most Likely Diagnosis

• Viral Upper Respiratory Infection (URI): This is the most common cause of mild URI symptoms and can sometimes present with chills in the absence of fever. The lack of fever does not rule out a viral infection, as not all viral infections cause fever.

Other Likely Diagnoses

• Allergic Rhinitis: Can cause URI-like symptoms such as sneezing, runny nose, and congestion, and may be accompanied by chills due to the body's allergic response.
• Sinusitis: An inflammation or infection of the sinuses can cause URI symptoms and chills, even in the absence of fever, especially if the infection is viral or if it's in its early stages.
• Influenza: Although influenza typically presents with fever, some cases, especially in older adults or those with compromised immune systems, might not have a fever. The presence of chills and URI symptoms could still suggest influenza.

Do Not Miss Diagnoses

• Pneumonia: While typically presenting with fever, pneumonia can occasionally present without fever, especially in the elderly or immunocompromised. Chills and mild URI symptoms could be early signs.
• Endocarditis: A bacterial infection of the heart valves, which can present with non-specific symptoms including chills, even in the absence of fever. This diagnosis is critical to consider due to its high mortality rate if untreated.
• Sepsis: Although sepsis is often associated with fever, it can also present without fever in some cases, particularly in the elderly or those with compromised immune systems. Early recognition is crucial due to its high mortality rate.

Rare Diagnoses

• Lymphoma: Certain types of lymphoma can cause systemic symptoms including chills, without fever, due to the body's immune response to the cancer.
• Tuberculosis (TB): TB can present with a wide range of symptoms, including chills and mild respiratory symptoms, and may not always be accompanied by fever, especially in its early stages or in immunocompromised individuals.
• Brucellosis: A zoonotic infection that can cause non-specific symptoms including chills, fever (though not always present), and URI-like symptoms. It's rare but important to consider in individuals with exposure to animals or their products.