Tuesday, 14 October 2008

Dr Lo -- Infectious Disease Conferences

Dear Bloggers

Dr Lo from the United States is back in Japan partaking in his annual infectious disease conferences. He has started his lecture series at CH which will continue for a week after which he will go to SK.

For his initial conference, he was presented a case of a patient with pneumonia of unknown aetiology.

Dr Lo made some excellent points during his lecturing which included:

  • When doing presentations in English, not using abbreviations for antibiotics e.g. PIPC = piperacillin, CTRX = ceftriaxone, as foreign physicians do not understand such abbreviations as they are not used in other countries.
  • Sputum examination for acid fast bacilli cannot completely rule out the presence of TB as the load of tuberculous bacilli organisms may be low despite active infection.
  • Use of single agents to treat TB can lead to negative smears and negative cultures and can complicate trying to make the diagnosis of mycobacterial infection.
  • If possible, always look back at the old radiology e.g. chest xrays, to see if there are any changes on current xrays to differentiate between acute and chronic changes
  • Legionella antigen testing of the urine will only pick up 75% of Legionella infections (serotype 1); hence, a negative test cannot completely rule out Legionella infection.
  • PCR for mycobacterium infection can be variable due to a lack of standardisation. There can be false positive results associated with the test. Hence, it is not a perfect test :-(
  • It is important to find out how previous TB was treated e.g. lung operation, antibiotic history (types of antibiotics used, dose and for how long); inappropriately used antibiotic regimens can result in under-treatment of TB and it is conceivable that reactivation can occur in the future.
  • Quantiferon test for TB cannot determine if a patient has active or latent TB. The blood needs to be processed rapidly and a negative test might result from blood not being processed within the obligatory time! Hence, a negative test might be due to inappropriate handling of the sample! Interestingly, the Quantiferon test is specific for TB and it will not detect other mycobacterial infections making it a unique test for TB identification albeit if the history fits the scenario. Lastly, a previous vaccination with BCG will not affect the result of this serum test. In some cases of indeterminate tuberculin skin testing, a Quantiferon test can be helpful to know if the patient has TB or not.
Dr Lo also went on to discuss about the aspects of Fever of Unknown Origin.

FUO is a defined as a fever of more or equal to 38.3 degrees Celsius for more than 3 weeks after investigation as an inpatient for 3 days or 3 outpatient visits with investigations; this is the Rule of 3's for remembering the definition of FUO.

After an interlude, Dr Lo talked further on infection control of tuberculosis. The following is a summary of his talk with additional facts from further reading.

  • Firstly, Japan has the highest incidence of TB among the G8 countries!
  • TB is an airborn infection (less than 5 micrometers in size) allowing it to circulate in the air for several days after expectoration. Droplets, on the otherhand, are larger than 5 micrometers and if spread from coughing, sneezing, talking or during invasive procedures, then the perimeter of infection is about 1 metre.
  • Droplet spread infections: patients should be in a private room. No negative pressure required. Door can be open! Close contact with patient requires wearing a mask. Droplet spread diseases include: neisseria meningitis, Haemophilus influenza, SARS, Burkholderia pseudomallei, Legionella spp, Aspergillus spp.
  • Airborne infections e.g. TB, Varicella zoster virus, influenza, measles, infection can occur several metres away from where they are produced. Patients need to be in a negative pressure room e.g TB. High efficiency filtration is necessary. Door MUST be kept closed. Medical staff and relatives need to wear an N95 mask. If patients need to be moved from their room, patients need to wear a mask as well. Any transportation around the hospital should be kept to a minimum.
  • Negative pressure rooms to prevent spread of TB are essential. In the absence of a negative pressure room, ideally the patient should be referred to an institution that does have such facilities.
  • Patients should be routinely asked if they have had TB exposure or infection, current symptoms and medical conditions that increase the risk for TB e.g. HIV. This comes back to proper history taking!
  • In the USA, in view that BCG is not used, if a PPD / tuberculin skin test is positive (>10mm), then asymptomatic healthcare workers need to be treated for latent TB. However, in those who have been vaccinated, it may be positive in the absence of active TB infection. In HIV+ or immunocompromised patients, a PPD skin test of >5mm is considered positive for active TB.
  • Interestingly, when the BCG vaccine is given before 5 years of age, the PPD skin as an adult would be expected to be negative whereas after the age of 5, it might be expected to be positive. Hence, when asking about vaccination, it is essential to know what age it was given!!! :-o
  • Latent TB is usually treated with a single drug whereas active TB requires 3-4 drugs.
  • So, what do we do when we have an asymptomatic patient in Japan or the UK who has previously been vaccinated with BCG but develops a positive PPD (tuberculin) skin test? For health care workers a positive test would equate to more than 10mm and for an asymptomatic member of the general public more than 15mm (the latter because they are at less risk from TB exposure). In the absence of symptoms this would be regarded as Latent TB which needs to be treated whereas if there are the usual symtpoms of cough, sputum, weight loss, night sweats and culture / microscopy / other confirmatory tests are positive then this is active TB which requires Urgent treatment.
  • Basically, there are many authorities who regard the BCG as useless to prevent TB and if positive, then this should be taken to indicate TB infection and with treatment commenced accordingly.
  • However, the efficacy of the BCG has been equated to about 80% at best and at worst 0% ! A 60 year study in American Indians showed that those who received BCG vaccinated developed less TB compared to those who were unvaccinated with an efficacy of about 50%. Moreover, a study from Africa in children who were vaccinated for TB confirmed that there was less TB in those children with BCG scars than in those without.
  • Hence, it is clear that BCG has some protective benefit but it does not prevent one from getting the disease! It is thought that it may reduce the frequency of disseminated (miliary) TB and intracerebral infection particularly in children.
Today was a great day for the residents to learn from an expert on infection.

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