When the severity of pneumonia is very severe, there can also be a decrease in white blood cells, which often suggests a higher possibility of severe pneumonia. Additionally, another scenario is viral pneumonia, where a decrease in white blood cells can also occur due to viral infections. Furthermore, there are special cases of infection, such as tuberculosis or infections caused by Mycoplasma or Chlamydia, where the use of anti-infection medications might also lead to a decrease in white blood cells. Another situation is when a patient inherently has a low white blood cell count, leading to weakened immunity and subsequently contracting pneumonia. In such cases, white blood cell counts might also not be high. Hence, severe bacterial pneumonia and decreases in white blood cells are relatively common in viral infections.