We found that 14.4 % of TB cases were not reported to a public health department and the proportion of unreported cases ranged between 0 and 45.2 % according to healthcare facility. It is notable that the five healthcare facilities that reported 100 % of their TB cases to the public health department employed a nurse case manager who acted as a liaison between the medical team and the infection control team, assisted with data collection, contact tracing, and case reporting to the public health department.
Previous studies in Europe have estimated the rate of unreported TB cases is over 20 % [7, 10, 11, 18, 19]. A rate of 27 % was described in central Italy , 38-49 % in the United Kingdom , and 80 % in Greece . Studies from Spain estimate rates of unreported TB range from 20 % to 46 % [13–15, 19], but these percentages represent a limited geographical area (the Baleares Islands, Area 15 of Alicante, León and Asturias). This range is wide and may be due to the local TB organization.
Regarding the factors associated with unreported TB cases, studies have described high rates of unreported cases among older patients [10, 13], among those without microbiological confirmation , among patients with absence of cavitary lesions on chest x-ray [10, 13], and among non-immigrant patients . Our study showed the same results on a bivariate level, but without statistical significance on a multivariate level for age, x-ray findings or country of origin. Retirement was associated with a higher risk of under-reporting, even independent of age. This has also been demonstrated in studies performed in other countries , which describe 25 % of unreported cases among patients over 60 years of age. This may be due to the higher rate of comorbidity conditions and multiple reasons for hospital admission, which could distract the provider that would diagnose and report the TB case.
We also found an association between unreported cases and extrapulmonary TB and smear-negative TB, for which the diagnosis may be delayed or without microbiological histology or culture. This was also described in many other studies [7, 10, 13, 20, 21], and maybe due to the fact that the provider think that transmission is lower among these cases. Nonetheless, reporting TB cases to the public health department is important to identify affected patients promptly thereby lowering transmission, to calculate an accurate incidence, and also to identify the TB index cases.
Smear-positive TB patients are more contagious and thus case reporting and contact tracing is crucial. Our study found that 9.4 % of smear-positive cases were not reported, which is actually lower than rates described in other studies .
The majority of the cases were diagnosed and reported from emergency departments and specialty clinics in our study as well as from other published studies [13, 15], and half of which were diagnosed in the emergency department. Case detection in the primary care setting is essential for early diagnosis and eventual disease control. We found that the diagnosis of TB in primary care centers is not associated with under-reporting (Table 3), which differs from one Spanish study . However the percentage of TB cases diagnosed in primary centers is small and could represent an initial opportunity for diagnosis that was missed. This suggests disease control in the primary care setting may be weak and could be a target for strategies to improve TB diagnosis. Training programs for the diagnosis of TB targeting the general public and primary care providers should be implemented.
When TB is not diagnosed or unreported, an opportunity to prevent disease transmission is lost and the disease can spread. All patients with a concern for TB should be immediately evaluated and the diagnosis should be reported to the public health department without delay [5, 6]. This requires coordination between the hospital, the department of epidemiology, and the microbiology and pathology departments. For example, electronic reporting systems, in which case reports are sent electronically from local to centralized databases, have been implemented in other countries [22, 23].
Our study also has limitations that are inherent to retrospective studies because of missing information. However, a prospective study design could have led to a bias of high compliance and reporting. The large number of participating healthcare facilities in our study offers a good estimation of unreported TB cases, even with a retrospective design. Additionally, the number of patients who were not evaluated at a specialty clinic is low. The patients who were diagnosed and followed by primary care centers have microbiological data recorded in a microbiology registry compiled with data from specialty clinics, but no electronic medical record.