Blood cultures are used to detect the presence of pathogens that result in infections. It is also used in deciding the correct course of antibiotic treatment. Blood cultures are, however, quite susceptible to contamination from external bacteria. This can be a disconcerting problem faced by laboratories and hospitals as bacteria outside of the patient cause contamination of the collected blood cultures. The blood cultures may be exposed to pathogens due to improper collection techniques by the specimen collectors. This can affect the results of tests done on the blood culture. As a result physicians may be led to believe that their patients suffer from serious conditions when in fact these results may have resulted from contamination by external pathogens. Such false findings can cause a great deal of concern for the patient, who may also have to undergo financial strain. The most common type of contaminant is that of the staphylococcus group of bacteria. Blood culture contamination results in high costs for the hospital as well due to the additional testing required, extended hospital stays and unnecessary treatment.
Contamination of blood culture cannot be avoided entirely, but the contamination rates may be reduced by taking certain steps. There have been several approaches taken which help to differentiate between bacteria that is clinically significant and contamination. Computer based techniques are also used increasingly nowadays to aid in controlling infection. There are also new techniques that have been developed which estimate bacteria risk and aid in reducing unnecessary use of blood cultures. Steps to prevent contamination include drawing blood culture samples from different venipuncture sites instead of intravenous catheters. Using the double needle technique also helps in preventing contamination, although this technique is now discouraged due to the risk of HIV transmission through the needles. The specialists or phleobotomists must also be dedicated and specially trained. Giving feedback regarding contamination rates to individual phlebotomists is another intervention that is usually done to prevent and reduce contamination. There are other steps that are also practiced and these result in a wide variation in contamination rates from one institution to another.
Many institutions also report an increase in the contaminants in the blood cultures. This is believed to result from the employment of new detection systems that are able to detect the contaminants in a more detailed and sensitive manner. Increase in the practice of culture collection from indwelling intravenous catheters is also believed to play a role in higher blood culture contamination rates.