The delay in TB diagnosis in one of the main risk factors for TB contagiousness as it is associated with inadequate implementation of respiratory protection measures and represents one of the main risk factors for TB spread [11, 12, 14, 15]. It can be divided into “patient delay” that is defined as the time from onset of TB symptoms to the first consultation with a health provider and “health care delay” that is defined as the time from the first consultation with a health provider to the initiation of treatment and “total delay” defined as the time from onset of TB symptoms to the initiation of treatment .
Factors associated with delayed TB diagnosis are heterogeneous and include demographic (older age, female) and socioeconomic factors (low income, low educational level) and clinical characteristics (negative sputum smear, smoking, sexually transmitted disease as comorbidity, less severe and atypical symptoms) . The ARTI of HCWS at our Institution during the study period was comparable to ARTI reported in the medical literature for high income countries with a moderate number of TB admissions, and it is estimated at around 1% (ranging from 0.2% to 12%) . The risk of LTBI dramatically increases when airborne protection procedures are not in place in the presence of active pulmonary TB, mainly due to delayed diagnosis, as demonstrated by the increased value of PEARTI compared with ARTI. It is interesting that the majority of index patients that elude a prompt diagnosis were Italian born patients who had a chest-x ray that was negative for cavitary lesions and was not specifically indicative of TB disease. Due to the combination of epidemiological and radiological issues, the suspicion of clinicians was low and therefore the patients were initially misdiagnosed.
In a recent paper published by Italian authors and conducted in the Emilia Romagna region, where TB epidemiology is similar to the Lombardy region, where our hospital is located, the median health care delay in TB diagnosis was significantly higher for Italian as compared with foreign born patients (60 vs 18 days) . It seems that Italian clinicians in general, show a higher suspicion index for migrants than for Italian born patients. Italy has a low incidence of TB with 7.6/100.000 patients reported in 2008 . In some industrialized areas, however, as in Lombardy the incidence reported was 13/100,000 population, and TB is increasingly associated with specific population subgroups: immigrants from countries with a high endemic infection, elderly Italian natives and the homeless. The majority of TB patients in Italy are foreigners aged 25–34 and, less frequently, older (>65 year) Italian citizens .
Among variables analyzed (gender, occupation, time since hire, history of BCG vaccination, positive sputum smear of index patient), only older age was associated with PEARTI. Age is a known risk factor for LTBI infection among HCWs [22, 23], possibly because it is associated with a longer period of direct contact with patients. This observation might suggest a limitation of the study, as PEARTI was measured as TST conversion three months after the exposure following a first negative TST result. This may represent a “booster effect”, an increase in the size of the induration produced by the Mantoux test due to the repetition of the test and secondary to the stimulation of cellular immunity in the absence of new M. tuberculosis infection . However, also taking into account the possibility of a booster effect of about 15% , these data underscore the high infectivity of a misdiagnosed TB patient admitted to a hospital. Moreover, in the univariate analysis the history of BCG vaccination was not associated with TST conversion neither at T1 nor at T2. It is important that clinicians always maintain a high level of suspicion associated with knowledge of local TB epidemiology in order to avoid delayed diagnosis and TB spread among HCWs and other contacts (relatives, friends, colleagues etc.). Our data of TST conversion after unprotected exposure to TB patients are consistent with those recently reported by Harris and coworkers . The exposure to an unrecognized Tb patient had as a consequence a TST conversion for 8% of staff members of a long term care facility, and two secondary cases of pulmonary TB among patients . These data underscore the infectiveness of pulmonary TB and the necessity of a the importance of considering TB when evaluating patients with pulmonary symptoms, particularly when symptoms persist or recur regardless antibiotic treatment .
Other limitations of the study are represented by the possibility of intra/inter reader errors in evaluating TST results, but as we considered as positive an induration equal or above 10 mm, and as the team has standardized methods, the possibility of different interpretation of the same TST result should be exiguous. Moreover, a HCWs could have been infected with M.tuberculosis outside the hospital, in the same timeframe. It not possible to rule out this hypothesis, but considering the epidemiology of tuberculosis in our region and the value of ARTI, the probability is low.