Community-Acquired Pneumonia (CAP): The presentation of fever, productive cough, body pain, elevated CRP (10mg/dL), and neutrophilia (indicated by TLC of 13600 with neutrophil predominance) strongly suggests a bacterial infection. CAP is a common condition that matches these symptoms and laboratory findings, making it the most likely diagnosis.

Influenza: Although the duration of symptoms (10 days) is a bit longer than typical for influenza, it cannot be ruled out, especially if the patient has been experiencing a prolonged course or if there's a current outbreak. Influenza can cause similar symptoms and may lead to secondary bacterial infections.
Acute Bronchitis: This condition, often caused by a viral infection but sometimes by bacteria, can present with productive cough and body pain. The presence of neutrophilia might suggest a bacterial component, but acute bronchitis is generally less severe than pneumonia.
Chronic Obstructive Pulmonary Disease (COPD) Exacerbation: If the patient has a history of COPD, an exacerbation could present with increased cough, sputum production, and shortness of breath, along with systemic symptoms like fever and body pain.

Tuberculosis (TB): Although less likely given the acute presentation, TB can cause fever, cough, and body pain. It's crucial to consider TB, especially if the patient has risk factors (e.g., immunocompromised state, exposure history, or travel to endemic areas), as missing this diagnosis could have significant consequences.
Pneumocystis jirovecii Pneumonia (PCP): In immunocompromised patients, PCP can present with similar symptoms. It's a critical diagnosis to consider due to its high mortality rate if untreated.
Lung Abscess: A lung abscess could present with fever, cough, and body pain, and while less common, it requires prompt diagnosis and treatment to prevent serious complications.

Q Fever: Caused by Coxiella burnetii, Q fever can present with nonspecific symptoms like fever, cough, and body pain. It's rare but should be considered in individuals with exposure to livestock or contaminated products.
Psittacosis: This infection, caused by Chlamydophila psittaci, is transmitted from birds to humans and can cause pneumonia. It's a rare diagnosis but should be considered in patients with a history of bird exposure.
Fungal Pneumonia: In immunocompromised patients or those with specific exposures (e.g., to bird droppings), fungal pneumonia (e.g., histoplasmosis, cryptococcosis) could be a consideration, although it's less common than bacterial causes.