For many years the World Health Organisation (WHO) defined four treatment categories for TB.1“Treatment of Tuberculosis - Guidelines for National Programmes”, WHO 1997
Category 1 was for new smear positive patients with pulmonary TB.
Category 2 was for sputum smear positive patients who have relapsed, who have treatment failure or who are receiving treatment after treatment interruption.
Category 3 was for new smear negative pulmonary TB patients (other than those in Category 1), and patients with new less severe forms of extra pulmonary TB.
Category 4 was for chronic cases who are still sputum positive after supervised re-treatment.
Redefinition of Categories 1-4
Over a number of years the original one to one correlation between patient group and treatment regimen was lost as Categories 1-4 were redefined with the increased availability of drug susceptibility testing. Also the same treatment regimen came to be recommended for patients in Categories 1 and 3.
Different treatment regimens also came to be recommended for patients in Category 2 depending on drug resistance.
Ending treatment categories
The third edition of the WHO TB treatment guidelines published in 2003 was the last to refer to Categories. The fourth edition of the WHO Treatment of Tuberculosis Guidelines published in 2010, abandoned reference to Categories 1-4 which had previously been used to prioritize patients for treatment.
Historically the greatest emphasis of TB control activities had been on the most infectious patients, those who had sputum smear positive TB, that is Categories 1 and 2. Smear negative TB patients were assigned third priority and MDR TB patients fourth priority.
For treatment decisions it no longer made sense to assign third priority to smear negative patients given their high mortality if they were living with HIV. Equally MDR-TB patients were assigned fourth priority despite the fact that they had such high mortality and they were responsible for the spread of the deadliest TB strains.
The Stop TB Strategy had an emphasis on universal access for all people with TB to high quality patient centred treatment. The Patients Charter for TB Care specified that all TB patients have "the right to free and equitable access to TB care, from diagnosis through treatment completion."
To replace categories 1-4, patients and their treatment regimens were subsequently grouped according to their likelihood of having drug resistance. New patients are differentiated from those who have previously had treatment.
Category 2 regimen
Treatment Category 2 was the regimen previously recommended by WHO for TB patients who required retreatment. For example due to treatment interruption or recurrence of disease. The preferred regimen was 2HRZES/1HRZE/5HRE (see the TB drugs page for the meaning of the abbreviations).
Category 2 regimen references
For a number of years after the the main WHO documents stopped referring to Treatment Categories, there were still occasional references in WHO and other documents to treatment Category 2. For example in the WHO 2017 TB Treatment Update it says.
"In patients who require TB retreatment, the category 2 regimen should no longer be prescribed and drug susceptibility testing (DST) should be conducted to inform the choice of treatment regimen (Good practice statement)".
This is rather confusing for some readers of this statement who were previously unaware of the existence of treatment categories. It is hoped that this terminology will soon be phased out.
TB categories and Streptomycin
A major problem with the Treatment category 2 regimen was that Streptomycin was being added to a regimen which a patient had previously been treated with. This goes against the principle of never adding one single drug to a failing regimen.
The drug Streptomycin which has toxic side effects such as causing deafness, was being given to patients who might well have drug susceptible TB. And Streptomycin was also potentially being given to patients who needed a properly defined MDR-TB regimen.