Ever so often, a patient or family member asks me “how do you know when the infection is gone? Are you going to repeat the cultures to see that they are negative?” My answer is usually the same – no, I don’t need to run a specific test for infection, such as a culture, to conclude that the infection is gone.
What I do look at, to assess for resolution of the infection, is a combination of subjective and objective factors, including the patient telling me that they feel better, resolution of fever, decreased pain and redness of any infected area, and improvement in certain lab parameters such as the white blood cell (WBC) count.
Here in more detail, are 8 parameters that tell us an infection is going, going, gone!
1. Feeling better – The patient starts to feel better in general, less malaised, achy, fatigued, out of sorts
2. Improved appetite – sick people often do not eat, they just don’t feel like it. For me, a returning appetite is always a very reassuring sign.
3. Decreasing pain – If infection was localized to a certain area, for example, if there was an abscess to the leg, the pain to the area starts improving and eventually totally resolves
4. Resolved fever – usually, no more fever for 2-3 days is a very good sign
5. Resolving redness and warmth, healing of a wound – If the infection was localized to a specific area, such as infected leg, with redness, warmth, etc, those signs start improving and eventually resolve. IF there was pus, eventually that stops draining and any wound that was present starts to heal.
6. White blood cell count (WBC) gets back to normal – You may remember that WBCs help fight infection and the value of the WBC count tends to be high in the early stages of an infection. As the infection resolves, the WBC count trends down to normal.
7. Improvements in other blood tests – Other blood tests which may be high in infection include the ESR (sedimentation rate) and CRP (C-reactive protein). These tests are markers of inflammation in the body. Usually, if there is a bad infection in the body, this causes a lot of inflammation, and the ESR and CRP tend to be high but gradually decrease to normal as the infection resolves.
8. Negative cultures – There are only a few infections where we actually repeat cultures (that’s the specific test to grow germs in the lab).
One example of a situation where we will specifically repeat cultures, is infection in the blood stream (blood poisoning). Because germs in the blood stream can potentially ‘stick’ or ‘lodge’ anywhere in the body if it lingers for too long, we need to know when the blood is sterile, and from that we calculate the duration of antibiotic therapy, which varies depending on the type of germ in the blood.
Another example of a situation where cultures are repeated to ensure that the infection is completely gone, is an infection an artificial joint. It has to be shown that there is no more infection, before the new joint is placed.
Knowing when an infection has resolved requires a physician to review a combination of factors, both subjective and objective. Not to be underestimated, is the patients own report of how they feel in general, compared to when they first came down with the infection.
In terms of duration of treatment, there are standard guidelines for duration of treatment of various infections, based on clinical experience over the decades.
As a side note – one thing I have noticed over time, is that when patients start feeling better, they start wearing their glasses again! I always take that as a positive sign. Another observation which a nurse mentioned to me, is that older patients, especially women, ask for their dentures when they start feeling better! Interesting observations, huh?