Staphylococcal infection (e.g., furuncle or carbuncle): This is the most likely diagnosis due to the common presentation of pus drainage, which is often associated with Staphylococcus aureus infections. These infections can cause localized abscesses or more extensive infections like furuncles (boils) or carbuncles.

Streptococcal infection: Streptococcal species, particularly Group A beta-hemolytic streptococci, can cause skin infections that may present with pus drainage, such as impetigo or ecthyma.
Folliculitis: An infection of the hair follicles, often caused by Staphylococcus aureus, which can lead to pus-filled bumps on the skin.
Cellulitis: A bacterial infection of the skin and subcutaneous tissues, usually caused by Streptococcus or Staphylococcus species, which can present with signs of infection including pus drainage in more severe cases.

Necrotizing fasciitis: A severe infection of the fascia, the tissue that covers muscles, which can rapidly progress and is life-threatening. Early signs may include severe pain, swelling, and redness, with possible pus drainage.
Gas gangrene (Clostridial myonecrosis): A severe, potentially life-threatening infection caused by Clostridium species, characterized by gas production in tissues, which can lead to severe pain, swelling, and drainage.
Actinomycosis: A chronic bacterial infection caused by Actinomyces species, which can form abscesses that drain pus and may mimic other conditions.

Cutaneous tuberculosis: A rare form of tuberculosis that affects the skin, which can cause lesions, ulcers, or abscesses with pus drainage.
Sporotrichosis: A fungal infection caused by Sporothrix schenckii, typically acquired through skin inoculation, which can cause nodular lesions that may ulcerate and drain pus.
Atypical mycobacterial infections: Infections caused by mycobacteria other than those that cause tuberculosis or leprosy, which can cause skin lesions or abscesses with pus drainage.