AIDS TREATMENT UPDATE, September 1995
Keith Alcorn

The mycobacteria that cause tuberculosis (called M.Tb) is transmitted in droplets expelled by coughing, and people who spend extended periods of time in close proximity to individuals with active tuberculosis are at risk of infection. Casual contacts of people with M.Tb are much less likely to become infected. In the UK a BCG vaccination will give a high level of protection to HIV-negative individuals.

Dr Anton Pozniak of Kings College Hospital, London, says that whilst the risk of infection with M.Tb is the same for HIV-negative and HIV-positive people (probably about 50% for household contacts), the chances of people with HIV developing active M.Tb once infected are much, much greater. "Once infected with M.Tb, the lifetime risk for an HIV-negative person of developing tuberculosis is about 10%. For an HIV-positive person it's 50-100%", he said.

MDR-TB is no more infectious than other strains of tuberculosis, but it is even more harmful to people with HIV than other strains. Diagnosis and appropriate therapy within a few weeks of infection are crucial to the effectiveness of treatment in HIV-positive people, says Dr Pozniak.

Tuberculosis is described as multi-drug resistant if mycobacteria resistant to the first line tuberculosis treatments can be isolated from a patient. Multi-drug resistant strains are thought to develop when an individual does not complete a course of anti-tuberculosis drugs, allowing resistance to emerge. 42 prior cases of MDR-TB, of which 38 were HIV-negative, have been reported in the UK.

OUTBREAK

The Chelsea and Westminster outbreak occurred after a patient underwent a sputum induction (a procedure where a salt water mist is breathed into the lungs, causing the patient to cough up sputum from deep in the lungs) on an open ward.

"The patient had been diagnosed with TB of the lymph node in Portugal, but not with pulmonary TB. We had no reason to believe that he had pulmonary TB and his symptoms suggested PCP rather than TB" said Dr Mark Nelson of the Chelsea and Westminster Hospital.

In future sputum inductions will be conducted in a single room off main wards, and people with MDR-TB will be nursed in single rooms with negative pressure ventilation which means that the air is pumped out of the room. A further four beds are being built, but Dr Nelson admits that the recent outbreak is speeding up this work.

Public health officials contacted by AIDS Treatment Update said that they had warned of the potential for such an incident at one of London's HIV centres, but hospitals did not give the danger a sufficiently high priority. "At the end of the day it is a matter of money - large hospitals do not have the funds to do all they want, and up until now London hospitals have not perceived MDR-TB to be a genuine risk to patients or staff" said one doctor.

Identification of hospital patients who may have pulmonary tuberculosis is very important for infection control. Dr Pozniak says that "If a patient who has lived in Southern Europe, Africa or Asia presents with a prolonged cough or respiratory illness it should be treated as TB until proven otherwise since the prevalence of TB in these regions is so high. In persons who have lived all their lives in the UK and who don't have known contacts with TB, the likelihood of TB is very much lower. The problem is that TB can resemble pneumonia and may not always be spotted until it's too late."

Dr Nelson points out that up to 80% of people with HIV are likely to be coughing for some reason and it is impossible to isolate them all before a full diagnosis.

ISOLATION

Clinics are now wrestling with the problem of how soon patients with MDR-TB can be released from hospital. Dr Nelson says "It can be very difficult to determine when patients are infectious. We test the sputum for signs of M.Tb, but if a person is sputum negative, are they truly non-infectious? In HIV-positive MDR-TB cases, people can swing from sputum positive to sputum negative to sputum positive unpredictably. We don't know how long an individual should stay in hospital after they test sputum negative before we can be certain that they are non-infectious. I know of one HIV-negative case of MDR-TB who has been in isolation for eighteen months."

A protocol for the clinical management of MDR-TB is available from the US Centers for Disease Control and Prevention (CDC) on the Internet at http://www.cdc.gov/diseases/tb.html.

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