HACEK is the acronym commonly used to describe and help doctors to remember a group of fastidious Gram-negative bacilli which normally live in the mouth, but which can also cause infective endocarditis. They are not common; less than 3% of endocarditis is caused by HACEK bacteria. More commonly endocarditis is caused by Alpha-haemolytic Streptococcus sp. (previously known as Viridans Streptococcus sp.), Enterococcus spp. and Streptococcus spp.
Click image to go to a great blog with many cartoon bacteria
So why blog about HACEK then? Well, firstly because I have just diagnosed a patient with HACEK endocarditis, and secondly because the names of the bacteria have changed recently and I was asked by a colleague to justify the
continuing use of HACEK endocarditis as a term. My immediate thoughts were of places I have worked where the people pronounce “how” as “ow”or “what” as "wat”...so why not a silent “H”, “HACEK” as “ACEK”...The silent “H” explanation got a raised eyebrow...OK, OK maybe “ACEK” is not an appropriate microbiology term! I’ll think on that...
The patient had a congenital heart defect and presented with pyrexia of unknown origin (PUO) 3 weeks after a bad upper respiratory tract infection. His blood cultures at the time were negative and because his serology showed a recent or acute EBV infection this was thought to be the cause of the PUO. However, he didn’t really improve and continued to have high fevers and rigors. He was discussed with me when re-admitted for further investigations and
we started to consider possible endocarditis. It transpired that the patient had been started on amoxicillin a few days before the original blood cultures were taken and this was a likely reason for them to be negative.
Sure enough, on repeat blood cultures 4 sets were positive with a small Gram-negative bacillus which identified as Aggregatibacter aphrophilus in all 4 sets which is a major criterion in the Dukes criteria which along with 3 minor criteria (fever, predisposing heart condition and haematuria as evidence of glomerulonephritis) confirmed the diagnosis of infective endocarditis and allowed appropriate treatment to commence.
This case is a great example of why microbiologists advise not starting antibiotics straight away if infective endocarditis is suspected, and only starting once at least 3 sets of blood cultures are taken. It is important to known what is causing the infection as long-term treatment depends on the identification of specific bacteria and antibiotic sensitivities. Starting antibiotics before the causative microorganism is known may cause confusion or delay the diagnosis and make the treatment more difficult. Treatment is long and arduous (normally involving multiple daily doses of IV antibiotics with respective monitoring of levels and hospitalisation for 4-6 weeks) so if less toxic antibiotics such as the penicillins or cephalosporins can be used, or easier regimes given, it is better for the patient in the long-term.
Back to the term HACEK. It was the identification of Aggregatibacter aphrophilus that sparked the discussion about whether HACEK is still a valid term to use because Aggregatibacter aphrophilus (which used to be called Haemophilus aphrophilus) along with Aggregatibacter paraphrophilus (which used to be called H. paraphrophilus)
represented the “H” in HACEK (see below). Now there is no longer an "H" in HACEK as they would be “A” for Aggregatibacter spp.
continuing use of HACEK endocarditis as a term. My immediate thoughts were of places I have worked where the people pronounce “how” as “ow”or “what” as "wat”...so why not a silent “H”, “HACEK” as “ACEK”...The silent “H” explanation got a raised eyebrow...OK, OK maybe “ACEK” is not an appropriate microbiology term! I’ll think on that...
The patient had a congenital heart defect and presented with pyrexia of unknown origin (PUO) 3 weeks after a bad upper respiratory tract infection. His blood cultures at the time were negative and because his serology showed a recent or acute EBV infection this was thought to be the cause of the PUO. However, he didn’t really improve and continued to have high fevers and rigors. He was discussed with me when re-admitted for further investigations and
we started to consider possible endocarditis. It transpired that the patient had been started on amoxicillin a few days before the original blood cultures were taken and this was a likely reason for them to be negative.
Sure enough, on repeat blood cultures 4 sets were positive with a small Gram-negative bacillus which identified as Aggregatibacter aphrophilus in all 4 sets which is a major criterion in the Dukes criteria which along with 3 minor criteria (fever, predisposing heart condition and haematuria as evidence of glomerulonephritis) confirmed the diagnosis of infective endocarditis and allowed appropriate treatment to commence.
This case is a great example of why microbiologists advise not starting antibiotics straight away if infective endocarditis is suspected, and only starting once at least 3 sets of blood cultures are taken. It is important to known what is causing the infection as long-term treatment depends on the identification of specific bacteria and antibiotic sensitivities. Starting antibiotics before the causative microorganism is known may cause confusion or delay the diagnosis and make the treatment more difficult. Treatment is long and arduous (normally involving multiple daily doses of IV antibiotics with respective monitoring of levels and hospitalisation for 4-6 weeks) so if less toxic antibiotics such as the penicillins or cephalosporins can be used, or easier regimes given, it is better for the patient in the long-term.
Back to the term HACEK. It was the identification of Aggregatibacter aphrophilus that sparked the discussion about whether HACEK is still a valid term to use because Aggregatibacter aphrophilus (which used to be called Haemophilus aphrophilus) along with Aggregatibacter paraphrophilus (which used to be called H. paraphrophilus)
represented the “H” in HACEK (see below). Now there is no longer an "H" in HACEK as they would be “A” for Aggregatibacter spp.
Click for larger image
The taxonomy of microorganisms is a bit of a nightmare and names are changing frequently. Most laboratories are pretty good at reporting the new names of microorganisms; adding a comment advising what the microorganism used to be called. This is helpful because published literature will have the old name, so if you try looking up a new name it won’t be there until new publications are written.
Whilst Haemophilus aphrophilus has changed, fortunately other new bacteria have been added to the list of causes of HACEK endocarditis, allowing me to feel justified in continuing to use the term (see below). I therefore declare I am not out-of-date, just simply using the term HACEK correctly based upon the new taxonomy! PHEW will that count towards “keeping up-to-date” for revalidation?
Whilst Haemophilus aphrophilus has changed, fortunately other new bacteria have been added to the list of causes of HACEK endocarditis, allowing me to feel justified in continuing to use the term (see below). I therefore declare I am not out-of-date, just simply using the term HACEK correctly based upon the new taxonomy! PHEW will that count towards “keeping up-to-date” for revalidation?
Click for larger image
But does this really matter? At the end of the day it is just an acronym of bacterial names referring to small Gram-negative bacilli from the normal oral flora which can
occasionally cause infective endocarditis. In fact the actual names don’t really matter that much as the treatment is the same regardless of the name.
Treatment is based upon how sensitive they are to antibiotics and should be guided by a Microbiologist. Empirical treatments exist for when microbiology results and
advice are unavailable and the patient is unwell (see the microbiology nuts and bolts book). Once a specific microorganism is known treatment should be adjusted
to target that specific microorganism. For HACEK endocarditis there are two main options (see below).
occasionally cause infective endocarditis. In fact the actual names don’t really matter that much as the treatment is the same regardless of the name.
Treatment is based upon how sensitive they are to antibiotics and should be guided by a Microbiologist. Empirical treatments exist for when microbiology results and
advice are unavailable and the patient is unwell (see the microbiology nuts and bolts book). Once a specific microorganism is known treatment should be adjusted
to target that specific microorganism. For HACEK endocarditis there are two main options (see below).
Click for larger image
Total Duration:
Native valve: 4 weeks
Prosthetic valve: 6 weeks
Gentamicin can be stopped after 2 weeks in both groups
So what are the key messages?
1. Try to hold off antibiotics in endocarditis if the patient is well enough because knowing the causative bacteria makes treatment much easier and safer.
2. The names of bacteria within the HACEK group have changed but HACEK is still applicable; familiarise yourself with the species names using the acronym and remember they can occasionally cause infective endocarditis.
3. Despite the changes in bacterial names, the treatment of HACEK endocarditis is still with Beta-lactam antibiotics such as IV Amoxicillin or IV Ceftriaxone PLUS IV Gentamicin.
Native valve: 4 weeks
Prosthetic valve: 6 weeks
Gentamicin can be stopped after 2 weeks in both groups
So what are the key messages?
1. Try to hold off antibiotics in endocarditis if the patient is well enough because knowing the causative bacteria makes treatment much easier and safer.
2. The names of bacteria within the HACEK group have changed but HACEK is still applicable; familiarise yourself with the species names using the acronym and remember they can occasionally cause infective endocarditis.
3. Despite the changes in bacterial names, the treatment of HACEK endocarditis is still with Beta-lactam antibiotics such as IV Amoxicillin or IV Ceftriaxone PLUS IV Gentamicin.
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