Most new immigrants with active TB are asymptomatic

More than 70% of new immigrants with active tuberculosis (TB) show no clinical signs or symptoms of the infection, and present with normal laboratory markers of inflammation, a study in Switzerland indicates.

This is a greater proportion than previously believed, report Gerd Laifer (University Hospital Basel, Switzerland) and colleagues, since earlier studies showed 50% of actively screened immigrants to be “symptom-free.”

Laifer et al looked at the 42,601 new immigrants who were screened for TB upon entry to one of five immigration centers in Switzerland. They enrolled the 112 with abnormal chest radiographs and compared them in a cohort study with 118 foreign-born residents from moderate-to-high incidence countries and 155 native residents presenting with suspected TB.

Active TB was confirmed in 40.5% of all patients: 38.4% of the new immigrants, 50% of the foreign-born residents, and 34.8% of the native residents.

Clinical signs of infection such as fever, night sweats, weight loss, cough, sputum production, and dyspnea were significantly less common in the new immigrants with active TB than in foreign-born and native residents with active TB.

Pulmonary auscultation was also less likely to be abnormal in the new immigrants compared with the two other groups.

But radiological presentation was similar in the three groups, apart from native residents having greater multilobular involvement.

Systemic inflammation markers, such as C-reactive protein and neutrophil counts, were only slightly elevated among new immigrants and normal in a substantial proportion (normal CRP in 73.8% and normal neutrophil count in 71.4%).

Both the other groups showed signs of systemic inflammation, with native residents having greater elevations in these inflammatory markers than foreign-born residents.

Overall, clinical signs and symptoms and inflammatory marker results were normal in more than 70% of new immigrants.

Finally, the proportion of positive M tuberculosis (MTB) tests was significantly lower in the new immigrants than in both foreign-born and native residents.

“The disappointing low yield of rapid tests for MTB underscores the diagnostic dilemma for this population and the need of a postmigration follow-up,” the authors write in the American Journal of Medicine.

They conclude: “New immigrants with TB detected in a screening program are often asymptomatic and have a low yield of rapid diagnostic tests but are at higher risk for resistant MTB strains.”