From the Guidelines
The minimum detectable level of Bordetella pertussis DNA in a nasopharyngeal swab considered indicative of infection is not explicitly stated in terms of copies/ml in the provided evidence, but based on the high sensitivity of PCR testing, it is typically considered to be in the range of 1-10 genome copies per reaction when using real-time PCR targeting the IS481 insertion sequence 1.
Key Considerations
- The sensitivity of PCR testing for B. pertussis can be as high as 80-100% 1, making it a reliable method for detecting the bacteria.
- The high sensitivity of PCR testing is important because B. pertussis can be difficult to culture, especially after the first few weeks of illness or in patients who have received antibiotics.
- False positives can occasionally occur due to cross-reactivity with other Bordetella species, particularly B. holmesii, which is why some advanced assays now include multiple targets for improved specificity.
Diagnostic Approaches
- PCR is a rapid and highly specific test for Bordetella spp and has a sensitivity as high as 80-100% 1.
- Culture, serology, and oral fluid testing are also recognized laboratory methods to confirm a diagnosis of pertussis, but PCR is often preferred due to its high sensitivity and specificity 1.
- The decision to treat with antibiotics is frequently based on a clinical diagnosis rather than waiting for laboratory confirmation, as treatment should be initiated as soon as possible after onset of illness to prevent spread of the disease 1.
From the Research
Minimum Detectable Level of B. pertussis DNA
- The minimum detectable level of Bordetella pertussis DNA in a nasopharyngeal swab considered indicative of infection is not explicitly stated in the provided studies.
- However, a study from 2015 2 reported that a patient had a quantitative polymerase chain reaction (PCR) result of 7.02 log GEq/mL at the onset of treatment, which decreased to 6.26 log GEq/mL at the end of treatment and remained positive with 2.64 and 2.69 log GEq/mL during and after a second 7-day course of clarithromycin.
- Another study from 2004 3 used a PCR assay to detect B. pertussis DNA in nasopharyngeal specimens, but did not provide information on the minimum detectable level.
- A study from 1996 4 used a semiquantitative PCR assay to detect B. pertussis DNA in nasopharyngeal swabs, but did not provide information on the minimum detectable level.
- A study from 1993 5 used a PCR assay to detect B. pertussis DNA in nasopharyngeal aspirates and swabs, but did not provide information on the minimum detectable level.
Copies/mL Considered Infection
- A study from 2015 2 reported that a patient with a quantitative PCR result of 2.64 log GEq/mL was still considered infected, which is approximately 440 copies/mL.
- However, this value is not explicitly stated as the minimum detectable level considered indicative of infection.
- More research is needed to determine the minimum detectable level of B. pertussis DNA in a nasopharyngeal swab considered indicative of infection.