During January–September 2008, a total of 16 TB cases were reported from three adjacent counties, including 14 cases linked to the outbreak (). Two people with TB (cases a and b) were reported in April, before the outbreak index patient (case 1) was reported. One of these (case a) was in a 5-year-old U.S-born female with Guatemalan parents who was identified during a contact investigation of a Guatemalan adult. Both case a and case b—a U.S.-born white male aged 40 years—were subsequently determined not to be part of the outbreak because they were infected with M. tuberculosis genotypes that did not match the outbreak strain.
Timing of TB cases in a Minnesota TB outbreak investigation, 2007–2008
The index patient (case 1) in the outbreak was a six-month-old U.S.-born male with Guatemalan parents whose family had arrived in the U.S. in 1997. He experienced four months of cough and fever that had begun in February 2008. TB was not considered at a medical visit in February in which the infant was treated with antibiotics (type unknown). He remained symptomatic and in May 2008, he was taken to the emergency department with coughing and night sweats, administered albuterol and antibiotics (type unknown), and discharged. Two days later he was hospitalized with pneumonia, had extensive consolidation of the right lung and limited pleural effusion on chest radiography, and a 10-mm-induration TST result; TB was diagnosed. Bronchoalveolar lavage fluid was culture-positive for M. tuberculosis susceptible to isoniazid, rifampin, ethambutol, and pyrazinamide.
The June 2008 investigation involving case 1 did not identify a source case, but revealed that both mother and father had evidence of TB infection (TST results for the mother and father were 20- and 22-mm induration, respectively). In addition, in the same household, all four siblings and two young cousins (aged 2–13 years) had active TB disease (cases 2–7) (). Five of the children did not have clinical symptoms but had positive TST results and evidence of TB on chest radiography or computerized tomography. One child (aged 2 years) had a negative TST result but had respiratory symptoms (cough and cold) and radiologic evidence of TB. All pediatric patients, including the infant index patient, began four-drug (isoniazid, rifampin, ethambutol, and pyrazinamide) DOT, and the parents began treatment for latent TB infection.
The same month, the presumed source for the children (cases 1–7) was identified when a 25-year-old Guatemalan-born male (case 8) was hospitalized with active pulmonary TB. His symptoms had begun in October 2007, and he had sought care at an urgent care facility in November 2007 for a fever and productive cough. Bronchitis was diagnosed, and he was prescribed an oral cephalosporin antibiotic, cough suppressant, and antipyretics. (Diagnostic evaluation had not included a TST or chest radiograph.) He remained symptomatic but did not seek further care until his condition deteriorated in June 2008, when he returned to the emergency department with a productive cough, fever, night sweats, and a 25-pound weight loss since January. He was medically transported from the local hospital to a regional hospital in which an airborne infection isolation room and infectious disease consultation were available. He had a negative TST result, but a chest radiograph revealed pulmonary infiltrates and a pleural effusion (). Sputum samples were acid-fast bacillus smear-positive and culture-positive for drug-susceptible M. tuberculosis. He began a four-drug treatment for TB and was discharged to continue DOT in July 2008.
Chest radiography of TB outbreak source case in a Minnesota TB outbreak, 2008
The contact investigation associated with case 8 identified multiple household, workplace, and social contacts. Of note, this patient was a singer in the music group managed by the father of the index patient (case 1). He had sung in the group during his entire infectious period (October 2007–June 2008). During this time, the group had played regularly at band members' homes (<20 people), the house of the index patient (<15 people), community centers (60–100 people), church services (maximum audience = 100 people), and other functions. Contacts of the case 8 patient were also identified in two households (seven people), at the patient's workplace (30 people), and other social settings (e.g., a sports team).
In July 2008, while the contact investigation associated with case 8 was ongoing, a 19-year-old Guatemalan-born male received a TB diagnosis (case 9) after he presented at a hospital with symptoms of a predominantly dry cough with intermittent hemoptysis, fever, 15-pound weight loss, and fatigue that began in March 2008. Although patients 8 and 9 did not name each other as contacts, they worked together, occasionally carpooled, and named common contacts. Patient 9 had not played in the band, visited the index patient's household, or participated in church community events. He reported not knowing anyone with TB or illness similar to his own.
Other cases were identified through contact investigations during July–September 2008. A 26-year-old Guatemalan-born male (case 10) who was a frequent visitor to the household of case 8 was also named as a workplace contact of case 9. The case 10 patient had a history of a medical visit for chest pain in February 2008 when a pleural effusion was documented. He returned in May 2008 with continued chest pain, but no cough or fever; he was referred to a pulmonologist but did not follow up. During these two medical visits, TB was not suspected. Then in August 2008, after the local health department recommended he have a TST as part of the ongoing TB contact investigations, and after experiencing epistaxis, dry cough, weight loss, and chest pain, he returned to the same facility that provided his initial medical care. TB was subsequently diagnosed on the basis of a positive TST result (15-mm induration), a chest radiograph that revealed bilateral perihilar infiltrates, and a sputum sample that was culture-positive for M. tuberculosis.
Four additional people were socially linked to the case 8 patient: an asymptomatic household contact aged 4 years (case 11) with a positive TST result (10-mm induration) and hilar adenopathy; two asymptomatic contacts aged 4 years (TST results 10- and 14-mm induration and infiltrates on chest radiographs) with multiple exposures to the band (cases 12 and 13); and a 37-year-old Guatemalan woman (TST result 10-mm induration and nodular infiltrates on chest radiograph) who occasionally visited the church (case 14).
Results of genotyping confirmed that the M. tuberculosis isolates from the singer (case 8) and two of his contacts (case 9 and case 10) matched the outbreak genotype (case 1) (i.e., PCR08788, or spoligotype 676177607760771 and MIRU 22432615332 [strain A]). Genotyping results of cases a and b demonstrated that they both differed substantially from the outbreak and each other (case a: PCR00226, or spoligotype 777777607760771 and MIRU 124326153324 [strain C]; case b: PCR00082, or spoligotype 777777777760771 and MIRU 223325154322 [strain B]).
In total, 150 contacts were identified who could be linked to the case 8 patient; 13 had secondary cases of TB disease and 62 had latent TB infection. The majority of cases were reported during June (). The prevalence of TB infection (either TB disease or latent TB infection) was greatest among foreign-born contacts compared with U.S.-born contacts, and greatest among household contacts, frequent visitors, and band members (). Foreign-born contacts were from Guatemala (n=65), Mexico (n=13), Honduras (n=2), and El Salvador (n=1); eight contacts did not report a country of origin. The number of years living in the U.S. was unrelated to TB infection for the 64 non-U.S.-born contacts who reported this information (median = 6 years; range: 1–24 years). Twenty contacts reported having a TST before this outbreak investigation. Although we did not collect information on visa status, 15 people in the investigation (contacts and patients) provided at least one pseudonym, creating a challenge for contact tracing by name. TB cases were more common among children, whereas the proportion with latent TB infection increased at older ages ().
Characteristics of contacts of TB patients investigated during an outbreak in Minnesota, 2008
All infected people received free treatment through county public health services. TB treatment was DOT and, as with contact investigations, required bilingual outreach workers.