You may not be missing anything. The preventive measures you mentioned are all very important and will serve you well. According to a recent (very large) study from the Kaiser Permanent system, the overall infection rate after anterior cruciate ligament reconstruction is fairly low (0.48 per cent). That is less than one-half of one percent.
In their study of 10,626 cases treated in 41 different medical centers around the United States, there were 51 total cases of infection (superficial and deep). There was a two-to-one (2:1) ratio of deep to superficial. Superficial infections only involved the skin and occur most often in the first 30 days after ACL reconstructive surgery. Deep infections can develop months to years later and involve the deeper soft tissue structures.
Further analysis of all the data also revealed that in most cases, hamstring tendon grafts were the source of both superficial and deep infections. Staphylococcus bacteria accounted for half of the deep and three-fourths of the superficial infections. More obese patients (higher body mass index) had a greater chance of developing a superficial infection. The reason for this is unknown but may be linked with the need to remove more soft tissue in larger patients.
What is behind this observed increase in superficial and deep infections associated with hamstring tendon grafts used for ACL reconstruction? There may be more than one possible avenue for this occurrence. The authors suggest the following possibilities. Contamination may occur during the harvest procedure itself or after harvest when the tendon graft is being prepared for use.
Hamstring tendon grafts take longer to prepare giving more time for possible contamination during graft preparation. And hamstring grafts require the use of a multifilament suture, which could be the source of the bacteria. If the graft or hardware used to fix the graft in place comes in contact with the skin, then contamination is more likely. And finally, the tools (e.g., screwdriver) used to insert the screws that hold the graft in place could be an external (environmental) source of contamination.
These are all external risk factors (i.e., have nothing to do with you or your body). You may want to let your surgeon know your concerns and questions. Knowing you have a delicate immune system may be useful information when selecting graft type and performing the technical aspects of the procedure. In the meantime, keep up the good efforts to aid your immune system. It won’t hurt you and may potentially contribute to a positive outcome.