My father-in-law was diagnosed with lung cancer about two to three months ago. He started chemo shortly after. A week ago he was sent to the hospital because he came down with pneumonia. While there, they found he had an infection with something called Pseudomonas. Could you please give me some information on that?

Penney

When bacterial pneumonia (infection of the lung) occurs in previously healthy persons it is usually caused by one of only a few different organisms. These bacteria can usually be treated easily with any of several common antibiotics. Pneumonia is also a common problem in people such as your father-in-law, who have lung cancer and are on chemotherapy. In these patients, there is a high risk of pneumonia caused by less-common organisms. These bacteria are said to be "opportunistic," which means that they usually do not cause disease in previously healthy people. This is similar to many of the infections in patients with AIDS -- those infections do not usually occur in healthy people.

Pseudomonas aeruginosa is one of these opportunistic bacteria. It would be very unusual for a previously healthy patient to develop this type of pneumonia. (This bacterium can cause minor skin infections in healthy people, however; the most common is associated with swimming pools, as the organism can survive in such settings. This infection usually gets better by itself and requires no treatment.) Pseudomonas pneumonia occurs most often in people with cancer, especially after chemotherapy, and in people on ventilators. It also occurs in patients with AIDS and chronic lung disease such as cystic fibrosis. In cancer patients, it can be a very severe infection. Symptoms include fever and cough, as well as shortness of breath. In people with a very weakened immune system, this infection may cause sepsis, severe whole-body disease, without an obvious source.

The problem with pseudomonal lung infections is that they do not respond to many of the antibiotics typically used to treat pneumonia in healthy patients. There are only a handful of appropriate choices. In addition, these choices are active against Pseudomonas in at most 90 percent of cases. Pseudomonas can even sometimes become resistant to an antibiotic during therapy, a situation that is unusual with most bacteria. For these reasons and others, we often use two antibiotics to treat suspected or proven pseudomonal infection, particularly if the infection is in the blood. It has been shown that the use of two antibiotics in pseudomonal bloodstream infection lowers the risk of death. This is especially true in seriously immunocompromised patients.