Guidelines on the Prevention and Control of Tuberculosis in Ireland

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<strong>Guidelines</strong> on the Prevention and Control of Tuberculosis in Ireland 2010HSE/HPSCpositive for AFB9 by microscopy is thought to be six to 10 times more contagious than a smear negativecase, while laryngeal TB cases are four to five times more contagious than smear positive pulmonarycases. 30;279Table 8.1: Definition of an infectious TB caseInfectious TB case• Sputum smear positive pulmonary TB• Laryngeal TBTB case presumed infectiousfor contact tracing purposes• BAL positive: (see below)The relative infectiousness of positive bronchial washings or BAL is unknown but some consider suchspecimens equivalent to sputum. 280 The US approach is to consider all BAL positive patients as infectious asthose who are sputum smear positive 51 (table 8.1). It is recommended that a precautionary approach shouldbe taken with BAL smear positive cases.Recommendation:• Infectious pulmonary and laryngeal cases are priorities for contact investigation. Aprecautionary approach should be taken with BAL smear positive cases• Those BAL smear positive cases with cavitation on chest X-ray, MDR-TB or XDR-TB or wherecontacts are immunosuppressed or are under 5 years of age should be presumed infectiousfor contact tracing purposes• The determination of infectivity of all other BAL smear positive patients should beconsidered on a case-by-case basis (clinical/microbiology/public health input).Radiographic findingsPatients who have lung cavities observed on a chest radiograph typically are more infectious than thosewith non-cavitary disease. 278;281;282 This is an independent predictor after bacteriological findings are takeninto account.AgeChildren younger than 10 years of age with pulmonary TB are rarely contagious because their pulmonarylesions are small (paucibacillary disease), cough is not productive, and few or no bacilli are expulsed. 109Generally, contact tracing investigations involving young children should be geared towards identifyingthe source and co-primary cases. However, although unusual, transmission from young children has beenrecorded. 283;284Recommendation:Young children under 10 years of age with pulmonary disease are rarely infectious. Suchcontact tracing investigations should be focused on finding a source and co-primary cases.Susceptibility of ContactsAgeChildren under five years of age are more likely to develop disease following recent infection. 110 Theincubation period is usually short, and severe forms of TB are common. Children under five years of ageshould be assigned a high priority for contact investigation.-95-
<strong>Guidelines</strong> on the Prevention and Control of Tuberculosis in Ireland 2010HSE/HPSCImmunosuppressionImmunosuppressed individuals should be assigned a high priority for contact investigation. TB patientswho are HIV-infected with low CD4 T-cell counts frequently have chest radiographic findings that are nottypical of pulmonary TB. Atypical radiographic findings increase the potential for delayed diagnosis whichincreases transmission.Indoor environmentTransmission is rarely thought to occur outdoors. Risk of transmission is greatest where there is prolonged,close contact with a case in an indoor environment; small volumes of shared indoor air, limited ventilationof the airspace with outdoor air and recirculation of air in closed circulation heating or air conditioningsystems. Indoor environments that are poorly ventilated, dark or damp, can lead to increased concentrationand survival of M. tuberculosis. 285-287Duration of exposure 281;288-290The likelihood of transmission of M. tuberculosis increases with the intensity, frequency and durationof exposure to a case. Usually it takes many hours or days to transmit an infectious dose, but casual/short exposures may lead to transmission if the case is infectious and environmental air conditions arefavourable. 291 Exposure duration of less than eight hours is generally considered not to be significant.Current US and UK guidelines 26;51 cite cumulative contact of eight hours or more for contact investigation.8.2 Initiating the Contact InvestigationPrompt notification of active TB cases is crucial, allowing for the early initiation of contact tracing (table8.2). Rapid evaluation of close contacts allows timely identification of those who have active disease and, ifactive disease has been excluded, allows initiation of treatment of LTBI for newly infected contacts beforedisease occurs.-96-
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Guidelines on the Prevention and Control of Tuberculosis in Ireland

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