Extrapulmonary TB is a significant health problem worldwide because of difficulties in its diagnosis and in monitoring its treatment. The proportion of extrapulmonary TB among all TB cases varies from country to country. Of the 22 high burden countries the highest proportion was reported from Cambodia (34.2%) and the lowest from China (0.69%) [5
]. The extrapulmonary manifestation of TB is prevalent in 10-34% of non-HIV cases while it occurs in 50-70% of patients co-infected with HIV [11
]. Ethiopia reports the third highest number of extrapulmonary TB globally (50,417) [5
]. In the current study, we assessed TB lymphadenitis, the major form of extrapulmonary TB, in a rural community in Ethiopia.
In this study the diagnosis of TB lymphadenitis was established when FNA smear microscopy for AFB, culture and/or cytology reported positive. In fact cytology suffers from low number of cells that are all in dispersion rather than organized tissue as in biopsies. Nevertheless, cytology is specific when compared against combined criteria [3
The prevalence of pulmonary TB was 76.1 per 100,000 people in the same study population during the same study period [12
]. It is higher than the prevalence of TB lymphadenitis as reported here. TB lymphadenitis accounted for 43.2% (95%CI: 28.7-59.1) of all forms of TB diagnosed in the study setting. A previous report from Ethiopia also indicated that TB lymphadenitis accounted for 40% of total TB cases in a rural health center [13
]. WHO estimates for Ethiopia that extrapulmonary TB accounts for roughly one third of the new cases of TB in the country [5
]. However, it is not possible to compare the findings from our study with the national figure of the WHO estimates because of two main reasons. First, the WHO data were derived from health institution based reports. Second, our study did not investigate all forms of extrapulmonary TB. Investigating the different parameters to identify risk factors for TB lymphadenitis in areas of high and low proportions in the country is recommended.
It has been reported that TB case detection remains very low in Ethiopia [14
]. Indeed, in our study all the TB lymphadenitis cases were newly diagnosed. The efforts to improve TB case detection in the country should be strengthened. It is logical that the health care seeking behavior could be low for TB lymphadenitis compared with that of pulmonary TB. This is mainly because pulmonary TB has a higher case fatality rate than TB lymphadenitis and the latter is mainly of cosmetic concern at least initially, which takes lower priority in rural communities with poor access to health facilities. Nevertheless, the health extension workers should be trained to identify not only pulmonary but also extrapulmonary TB suspects in the community and link them to health facilities.
A contact history with a chronic cougher was highly related with the odds of having TB lymphadenitis. This partly indicates that there is transmission going on in the community although further study may be needed to unravel the transmission dynamics. Moreover, this might indicate that the route of acquisition of lymph node TB is probably the same as pulmonary and can partly explain why Mycobacterium bovis
was not detected. Other studies have reported a predominance of Mycobacterium tuberculosis
in TB lymphadenitis in Ethiopia [15
] although bovine transmission would be expected where raw milk is consumed.
Cervical lymph nodes were the prominent sites involved in our study supporting previous reports [17
]. Studies have reported that women were more likely to be positive for TB lymphadenitis compared with men [20
]. Moreover, it has been suggested that in male dominated communities, where women experience poorer living conditions, young females generally notice differences in their appearance earlier than males [26
]. In our study, however, the rate of TB lymphadenitis was not significantly different between the two sexes. Our previous finding from the study area on health seeking behavior also did not find a difference in gender [27
]. The age group 35–44
years and FNA samples from axillary lymph nodes has shown the largest proportion of cases but difference in prevalence in terms of age group and location of the lymphnodes was not statistically significant.
Previous studies have suggested that the extrapulmonary forms of TB could be attributed to HIV co infection [18
]. In Ethiopia the HIV prevalence for rural areas was estimated to be 0.9% [29
]. However, in our case all the TB suspects were HIV negative. This suggests that apart from HIV either mycobacterial strains or host factors may play an important role in TB lymphadenitis in this community. Recent reports elsewhere identified that single nucleotide polymorphisms rs4893980 on gene PDE11A of chromosome number 2, rs10488286 on gene KCND2 of chromosome number 7 and rs2026414 on gene PCDH15 of chromosome number 10 in humans were associated with extrapulmonary tuberculosis [30
]. In this study we did not do the typing for host genetic factors predisposing for TB lymphadenitis.
The strength of our study was that it has tried to address the neglected component of TB at community level. However, our study was not without pitfalls. We probably underestimated the prevalence of tuberculous lymphadenopathies because individuals were not systematically examined for lymphadenopathies and culturing of the samples were delayed due to transport problems. Moreover, the methods that we used for the laboratory diagnosis of lymph node TB are not the most sensitive and specific. We did not use PCR which may have high sensitivity in detection of lymph node TB [31
]. These all limitations in combination may have resulted in under estimation of the lymph node TB prevalence in communities living in Gilgel Gibe research site.