Microbiology Case Study: A Routine Sputum Culture on a 20 Year Old Cystic Fibrosis Patient

Case History

A 20 year old woman with cystic fibrosis was routinely screened with bacterial sputum cultures.  The patient reported feeling well and was compliant with her treatment regimen.  She had no history of Nocardia colonization in the past and her last hospitalization was four years prior due to a pulmonary exacerbation in which cultures grew Stenotrophomonas and Pseudomonas.

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Image 1: Modified acid fast stain showing two unique traits of Nocardia: long, delicate rods and weak acid fastness.

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Image 2: Nocardia colonies on buffered charcoal yeast extract (BCYE) agar.

Discussion

Nocardia are slow growing, aerobic gram negative rods. Nocardia are unique for being weakly acid fast and displaying aerial hyphae.  They are ubiquitous organisms that can cause a variety of infections in immunocompromised individuals. Most often in the United States, nocardiosis causes a lung infection. If left untreated, it can spread to the brain or spinal cord, where up to 44% die [1].

The above patient showed no signs of an infection, making the possibility of colonization by Nocardia more likely.  Cystic fibrosis patients can be colonized by Nocardia and the clinical approach is to treat regardless of the patient’s overall health. However, there is a lack of reporting on whether Nocardia is the cause of an infection when it happens. Host and pathogen interactions are also not well known. Thorn et al. showed that treating cystic fibrosis patients that are colonized with Nocardia with oral antibiotics did not affect their clinical outcome [2]. More studies are needed to be done to see if antibiotics are warranted in circumstances like the above patient.

References:

  1. Nocardiosis. https://www.cdc.gov/nocardiosis/transmission/index.html
  1. Pulmonary nocardiosis in cystic fibrosis. Thorn, Shannon T. et al.. Journal of Cystic Fibrosis, Volume 8 , Issue 5 , 316 – 320

 

-Angela Theiss is a pathology resident at the University of Vermont Medical Center.

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-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Associate Professor at the University of Vermont.

Cystic Fibrosis Related Diabetes

Cystic fibrosis-related diabetes (CFRD) is a type of diabetes that affects individuals who have Cystic Fibrosis. CFRD is an entity unto itself, having several aspects that make it different from other forms of diabetes.

Cystic Fibrosis (CF) is one of the most common genetic defects among the Caucasian population, and it is a devastating, systemic disease. When CF was first being diagnosed, children with this disorder rarely lived to reach their teens]; now the average life expectancy  of an individual with CF is around 36 years. Still horrifically short, but better. The fact that people with CF are living longer means they acquire other disorders, including a type of diabetes. It has been shown that with increasing age in the CF population there is increasing incidence of diabetes mellitus.  Roughly 20% of adolescents with CF have diabetes and about 50% of adults with CF have CFRD (1).

CFRD is not as straight-forward to diagnose as type 1 and type 2 diabetes, so it’s important for laboratory professionals to be aware of this disease. People with CF who have diabetes may not always have hyperglycemia. Also hemoglobin A1c (Hgb A1c) values, which is a test recommended by the ADA for diagnosing diabetes, may not be elevated in these patients. The oral glucose tolerance test (OGTT) is recommended for diagnosis of CFRD, and yet even these results may be equivocal in CFRD patients (2). Nonetheless, the ADA/CFF guidelines suggest that all CF patients over 10 years of age should be screened yearly for CFRD using the OGTT. In addition, at least one study in the literature has found that when performing an OGTT on CFRD patients, a glucose level at the 1 hr time point correlates best with the patient’s lung function (3). Thus, if your lab performs OGTT on individuals with suspected CFRD, the physician requesting the test may want the glucose value on a one hour time point as well as the standard 2 hour OGTT.

Individuals with CF who get CFRD tend to have weight loss, protein catabolism, worsened lung function and significantly increased mortality compared to CF individuals without diabetes. The increased mortality is directly related to decreased pulmonary function, rather than to the atherosclerotic vascular disease seen in other types of diabetes. Insulin therapy is the recommended therapy for CFRD.

-Patti Jones

References:

  1. Moran A, Brunzell C, Cohen RC, Katz M, Marshall BC, Onady G, Robinson KA, Sabadosa KA, Stecenko A, Slovis B. Clinical care guidelines for cystic fibrosis-related diabetes.  Diabetes care 33(12):2697-2708. 2010.
  2. Rana M, Munns CF, Selvadurai H, Donaghue KC, Craig ME. Cystic fibrosis-related diabetes in children – gaps in the evidence? Nature Reviews: Endocrinology, 6:371-378. July 2010.
  3. Brodsky J, Dougherty S, Makani R, Rubenstein RC, Kelly A. Elevation of 1-hour plasma glucose during oral glucose tolerance testing is associated with worse pulmonary function in cystic fibrosis. Diabetes Care, 34:292-205. 2011.