Case definitions 2.1 Chapter objectives
2. CaSE dEfInITIonS
Extrapulmonary tuberculosis (EPTB) refers to a case of TB (defined above) involv- ing organs other than the lungs, e.g. pleura, lymph nodes, abdomen, genitourinary tract, skin, joints and bones, meninges. Diagnosis should be based on at least one specimen with confirmed M. tuberculosis or histological or strong clinical evidence consistent with active EPTB, followed by a decision by a clinician to treat with a full course of tuberculosis chemotherapy. The case definition of an EPTB case with sev- eral sites affected depends on the site representing the most severe form of disease. Unless a case of EPTB is confirmed by culture as caused by M. tuberculosis, it cannot meet the “definite case” definition given in section 2.3 above.
2.5 bacteriological results
Bacteriology refers to the smear status of pulmonary cases and the identification of M. tuberculosis for any case by culture or newer methods. Culture and drug suscep- tibility testing are discussed in section 3.8.1. For definitions of MDR-TB cases, see reference 7.
Standard 2 of the ISTC (5) states that all patients suspected of having pulmonary TB should submit at least two sputum specimens for microscopic examination in a qual- ity-assured laboratory. When possible, at least one early-morning specimen should be obtained, as sputum collected at this time has the highest yield. ISTC Standard 4 states that all persons with chest radiographic findings suggestive of TB should sub- mit sputum specimens for microbiological examination (5).
Smear-positive cases are the most infectious and most likely to transmit their dis- ease in their surroundings; they are the focus for infection control measures (2) and contact investigations (3). Bacteriological monitoring of treatment progress is most feasible and practicable in these patients (see Chapter 4).
It is also important to identify smear-negative cases, especially in persons living with HIV for whom mortality is higher than in smear-positive pulmonary TB cases (4). For diagnostic algorithms for smear-negative persons living with HIV, see reference 4. A case of pulmonary TB is considered to be smear-positive if one or more sputum smear specimens at the start of treatment are positive for AFB (provided that there is a functional EQA system with blind rechecking1).
The definition of a new sputum smear-positive pulmonary TB case is based on the presence of at least one acid fast bacillus (AFB+) in at least one sputum sample in countries with a well functioning EQA system. (See www.who.int/tb/dots/laboratory/ policy/en/index1.html.)
1 In countries without functional EQA, the definition from the third edition of these guidelines applies: a smear-positive pulmonary TB case was defined as one with:
a. two or more initial sputum smear examinations positive for AFB, or
b. one sputum smear examination positive for AFB plus radiographic abnormalities consistent with active PTB as determined by a clinician, or
Smear-negative PTB cases should either:
A. have sputum that is smear-negative but culture-positive for M. tuberculosis: • a case of pulmonary TB is considered to be smear-negative if at least two
sputum specimens at the start of treatment are negative for AFB1 in countries
with a functional EQA system, where the workload is very high and human resources are limited (see http:///www.who.int/tb/dots/laboratory/policy/en/ index2.html);
• in all settings with an HIV prevalence of >1% in pregnant women or ≥5% in TB patients, sputum culture for M. tuberculosis should be performed in patients who are sputum smear-negative to confirm the diagnosis of TB (4).
OR
B. meet the following diagnostic criteria: (6–8)
• decision by a clinician to treat with a full course of anti-TB therapy; and • radiographic abnormalities consistent with active pulmonary TB and either:
— laboratory or strong clinical evidence of HIV infection or:
— if HIV-negative (or unknown HIV status living in an area of low HIV preva- lence), no improvement in response to a course of broad-spectrum antibiot- ics (excluding anti-TB drugs and fluoroquinolones and aminoglycosides). Pulmonary TB cases without smear results are no longer classified as smear-negative (4); instead, they are recorded as “smear not done” on the TB register (6) and on the annual WHO survey of countries.
For patients suspected of having EPTB, specimens should be obtained from the sus- pected sites of involvement (Standard 3 of the ISTC (5)). Where available, culture and histopathological examination should also be carried out. Additionally, a chest X-ray and examination of sputum may be useful, especially in persons with HIV infection.
2.6 History of previous treatment: patient registration group
At the time of registration, each patient meeting the case definition is also classified according to whether or not he or she has previously received TB treatment and, if so, the outcome (if known). It is important to identify previously treated patients because they are at increased risk of drug resistance, including MDR-TB (see section 3.6). At the start of therapy, specimens should be obtained for culture and DST from all previously treated patients. Treatment depends on whether the patient has relapsed 1 And no specimen is smear-positive.
or is returning after default or after prior treatment has failed (see section 3.7). The distinctions between new and previously treated patients, and among the subgroups of previously treated patients, are also essential for monitoring the TB epidemic and programme performance.
New patients have never had treatment for TB, or have taken anti-TB drugs for less than 1 month. New patients may have positive or negative bacteriology and may have disease at any anatomical site.
Previously treated patients have received 1 month or more of anti-TB drugs in the past, may have positive or negative bacteriology and may have disease at any ana- tomical site. They are further classified by the outcome of their most recent course of treatment as shown in Table 2.1 below.
Patients whose sputum is smear-positive at the end of (or returning from) a second or subsequent course of treatment are no longer defined as “chronic”. Instead, they should be classified by the outcome of their most recent retreatment course: relapsed, defaulted or failed.
2. CaSE dEfInITIonS
Table 2.1 regiSTrATion group By ouTcome of moST recenT TB TreATmenT
registration group
(any site of disease) bacteriology
a outcome of most recent prior treatment (defined in Table 4.1)
new + or – –
Previously treated relapse + cured
Treatment completed
failure + Treatment failed
default + defaulted
Transfer in: A patient who has
been transferred from another TB register to continue treatment
+ or – Still on treatment
other + or – All cases that do not fit the above definitions, such as patients • for whom it is not known whether
they have been previously treated; • who were previously treated but with
unknown outcome of that previous treatmentb (3, 8); and/or
• who have returned to treatment with smear-negative pTB or bacteriologically negative epTBb (3) a + indicates positive smear, culture or other newer means of identifying M. tuberculosis
– indicates that any specimens tested were negative.
2.7 HIV status
Determining and recording the patient’s HIV status is critical for treatment decisions (see Chapters 3 and 5) as well as for monitoring trends and assessing programme performance. WHO’s revised TB Treatment Card and TB Register include dates of HIV testing, starting co-trimoxazole, and starting ART. These important interven- tions are discussed more fully in Chapter 5.
references
Engaging all health care providers in TB control: guidance on implementing public-
1.
private mix approaches. Geneva, World Health Organization, 2006 (WHO/HTM/
TB/2006.360).
WHO policy on TB infection control in health care facilities, congregate settings and
2.
households. Geneva, World Health Organization, 2009 (WHO/HTM/TB/2009.419). Implementing the WHO Stop TB Strategy: a handbook for national tuberculosis control
3.
programmes. Geneva, World Health Organization, 2008 (WHO/HTM/TB/2008.40). Improving the diagnosis and treatment of smear-negative pulmonary and extrapulmo-
4.
nary tuberculosis among adults and adolescents: recommendations for HIV-prevalent and resource-constrained settings. Geneva, World Health Organization, 2007 (WHO/
HTM/TB/2007.379; WHO/HIV/2007.1).
International Standards for Tuberculosis Care (ISTC)
5. , 2nd ed. The Hague, Tuberculo- sis Coalition for Technical Assistance, 2009.
Revised TB recording and reporting forms and registers – version 2006
6. . Geneva, World Health Organization, 2006 (WHO/HTM/TB/2006.373; available at: www.who.int/ tb/dots/r_and_r_forms/en/index.html).
Guidelines for the programmatic management of drug-resistant tuberculosis: emer-
7.
gency update 2008. Geneva, World Health Organization, 2008 (WHO/HTM/TB/
2008.402).
Global tuberculosis control 2009: epidemiology, strategy, financing. WHO report 2009
8. .