👉 Mastitis is a condition that occurs when an inflamed or infected lymph node becomes enlarged and painful. It's often associated with bacterial infections such as streptococcus pneumoniae, but it can also be caused by other factors like parasitic infections or viral infections. In the case of mastitis, the inflammation usually starts in the lower part of your body (the abdomen) where the lymph nodes are found. The bacteria that cause the infection enter the bloodstream and travel to the organs and tissues