Epidemiology of Mycobacterial Infections

National Institute Of Allergy And Infectious Diseases

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Abstract

Summary 1) Environmental and host factors A key aspect of our work over the past year has been to understand the relative contributions of host and environmental factors for infection and disease from the nontuberculous mycobacteria. To that end, we analyzed data related to mycobacterial infections among persons with cystic fibrosis. Persons with cystic fibrosis (CF) are at higher risk from NTM than the general population, with an estimated prevalence of 13%. In the first study, persons with CF were recruited from 21 geographically diverse CF centers nationally, and a nested cohort study was conducted whereby persons with incident mycobacterial infections (at least one prior negative culture followed by one positive culture) were age and sex matched to culture negative controls, and exposures to water and soil were assessed by a standardized questionnaire. Cohort prevalence at each of 21 centers was correlated with climatic conditions in the same area through linear regression modeling. Overall, 48 cases and 85 controls were enrolled. Indoor swimming was associated with incident infection (ORadj= 5.9, C.L, 1.3, 26.1), although only nine (19%) cases and five (6%) controls reported indoor swimming in the four months prior to infection. Exposure to showering and municipal water supply was common among both cases and controls: 77% of cases and 76% of controls reported showering at least daily. In linear regression, average annual atmospheric water vapor content was significantly predictive of center prevalence (p=0.0019), with R2=0.40. Atmospheric conditions explain more of the variation in disease prevalence than individual behaviors. The risk of specific exposures may vary by geographic region due to differences in conditions favoring mycobacterial growth and survival. However, because exposure to these organisms is ubiquitous and behaviors are similar among persons with and without pulmonary nontuberculous mycobacteria , genetic susceptibility beyond cystic fibrosis is likely to be important for disease development. Common individual risk factors in high risk populations remain to be identified. In a separate analysis, patient registry data from the Cystic Fibrosis Foundation (CFF) for 2010-2011 were analyzed to describe the prevalence and screening practices of NTM among U.S. CF patients aged >12 years old. Climatic data were also obtained and predictors of NTM infection analyzed using regression analysis. Geographic clustering and mycobacterial culture rates by state were also assessed. Among CF patients aged &#8805; 12 years, 58% had mycobacterial cultures; 14% were positive for NTM. Most states (n=31) had a prevalence of 10-20%; 7 states predominantly in the W and SE had a prevalence of &#8805;20%, including Alaska which cultured patients more frequently than any other state. Nearly 60% of positive cultures were for Mycobacterium avium complex, though this ranged by state, from 29% in Louisiana to 100% for Nebraska/Delaware. Significant (p<0.002) spatial clustering of NTM was detected centering in Wisconsin, Arizona, Florida, and Maryland. Higher saturated vapor pressure increased risk for NTM (OR=1.06, 95% CI: 1.02-1.10). The proportion of patients cultured for mycobacteria varied greatly by state of residence (median=46%; range: 9%-73%). These findings highlight that NTM prevalence varies significantly among CF patients by geographic area, and is largely influenced by environmental factors. However, NTM culture practices vary greatly, with some high-prevalence states screening <25% annually. Routine screening for all CF patients is needed for timely detection. 2) With respect to treatment for NTM pulmonary disease, we have analyzed natural history data from NIH to better assess the effectiveness of certain regimens. Treatment of pulmonary nontuberculous mycobacteria (PNTM), especially Mycobacterium abscessus, requires prolonged, multi-drug regimens with high toxicity and suboptimal efficacy. Options for refractory disease are limited. We reviewed the efficacy and toxicity of inhaled amikacin in patients with treatment refractory PNTM. Records were queried to identify patients who had inhaled amikacin added to failing regimens. Lower airway microbiology, symptoms, and CT scan changes were assessed along with reported toxicity. The majority (80%) of the 20 patients who met entry criteria were female; all had bronchiectasis, two had cystic fibrosis and one had primary ciliary dyskinesia. At initiation of inhaled amikacin, 15 were culture positive for M. abscessus and 5 for M. avium complex and had received a median (range) of 60 (6, 190) months of NTM treatment. Patients were followed for a median of 19 (1, 50) months. Eight (40%) patients had at least one negative culture and 5 (25%) had persistently negative cultures. A decrease in smear quantity was noted in 9/20 (45%) and in NTM culture growth for 10/19 (53%). Symptom scores improved in 9 (45%), were unchanged in 7 (35%), and worsened in 4 (20%). Improvement on CT scans was noted in 6 (30%), unchanged in 3 (15%) and worsened in 11 (55%). Seven (35%) stopped amikacin due to: ototoxicity in 2 (10%), hemoptysis in 2 (10%), and nephrotoxicity, persistent dysphonia, and vertigo in one each. In some patients with treatment refractory NTM, the addition of inhaled amikacin was associated with microbiologic and/or symptomatic improvement; however, toxicity was common. Prospective evaluation of inhaled amikacin for NTM disease is warranted. In a separate analysis, we evaluated the relationship between chronic macrolide use and pulmonary NTM infection among persons with cystic fibrosis (CF). Persons with cystic fibrosis (CF) are at high risk of nontuberculous mycobacterial (NTM) infection, with treatment requiring prolonged multi-drug regimens that include macrolides. While macrolides, specifically azithromycin, are used in the management of CF patients with chronic Pseudomonas, macrolide-resistant NTM infections are of growing concern. Further, a recent study suggested a possible link between long-term macrolide use in CF patients with an increased NTM infection rate, specifically theorizing that long-term azithromycin use may predispose CF patients to infection with M. abscessus by facilitating mycobacterial survival through the blocking of intracellular autophagy, the immune response needed to clear these infections. Clarifying the relationships between long-term macrolide therapy and NTM infections by species is vital for providing improved NTM treatment and prevention recommendations for the CF population, and provides insights into treatment for the non-CF population as well. The CF Patient Registry (CFPR) collects extensive data annually on >90% of all U.S. CF patients, including detailed mycobacterial data starting in 2010. We obtained data from the 2011 Cystic Fibrosis Patient Registry to further study patterns of NTM among CF patients and further address these issues. The 2011 CFPR included 27,112 patients; 5,403 (20%) were cultured for mycobacteria in 2010-2011 and met all inclusion criteria. Of these, 191 (4%) were NTM-positive in 2011 only (incident cases), while 5,212 (96%) were NTM-negative in both 2010 and 2011 (controls). Among the cases, 122 (64%) were culture-positive for Mycobacterium avium complex (MAC) and 69 (36%) for M. abscessus. Azithromycin use in 2010 was less frequently reported among MAC cases (57%; OR=0.7, p<0.05) and M. abscessus cases (51%; OR=0.5, p<0.01) than in controls (66%). Among adolescents and adults, patients with the greatest number of years on chronic macrolides were the least likely to develop incident NTM in 2011 (p<0.01). In summary, incident NTM cases were significantly less likely to have had prior long-term azithromycin use. To better understanding underyling genetic factors which may contribute to diseas