Minnesota Department of Health (MDH) Bug Bytes
March 8, 2002
Vol. 3: No. 4
1. Dr. Koch and World TB Day
World TB Day, March 24, marks the anniversary of the date in 1882 when Dr. Robert Koch announced the discovery of the tuberculosis (TB) bacillus. TB is the second leading infectious disease killer worldwide. Koch taught himself to read at age 5. As a country doctor, he became concerned he couldn't help his patients since he didn't know what caused their illnesses. His wife gave him a microscope in 1872, and by 1876, he had demonstrated that Bacillus anthracis was the cause of anthrax. By 1880 he had established the criteria for ascertaining the causative agent of infectious diseases, known today as Koch's postulates. In 1905, he was awarded the Nobel Prize for Physiology or Medicine "for his investigations and discoveries in relation to tuberculosis".
While the number of TB cases reported nationally has decreased each year since 1993, TB incidence in Minnesota is increasing. In 2001, 239 new TB cases (4.9 cases per 100,000 population) were reported. This represents a 34% increase since 2000 (178 cases) and the largest number of cases reported since the early 1970s. For the fifth consecutive year, TB incidence in Minnesota remains at or above the national goal (for the year 2000) of 3.5 per 100,000.
TB epidemiology in Minnesota also is distinct from that nationally, with the most significant factor being the high percentage of TB cases that occur among foreign-born persons. In 2001, 194 (81%) cases occurred in persons born outside the U.S. This trend reflects the unique and changing demographics of immigrant populations arriving here, particularly persons arriving from regions of the world where TB is prevalent. The most common regions of origin for foreign-born persons with TB disease reported in 2001 include sub-Saharan Africa (61%) (e.g., Somalia, Liberia, and Ethiopia) and South/Southeast Asia (24%) (e.g., Laos and Vietnam). More than half (55%) of foreign-born TB cases were less than 30 years of age, while the most common (36%) age group among U.S.-born cases was those 60 years of age or older. Other less frequent risk factors included homelessness (5%), HIV infection (3%), incarceration in a correctional facility (1%), and residence in a nursing home (1%). Twenty-eight (32%) of the state's 87 counties reported at least one TB case in 2001, with the majority (83%) being in the seven-county Twin Cities metropolitan area.
In 2001, there were 56 (29%) cases of drug-resistant TB, including 23 (12%) cases resistant to isoniazid, and 4 (2%) cases of multi-drug resistant TB (MDR-TB) (i.e., resistant to at least isoniazid and rifampin). This represents an increase in drug resistance overall and, most notably, among U.S.-born persons. The percentage of drug-resistance among foreign-born cases was relatively stable at 29%. However, among U.S.-born cases, the percentage of drug resistance more than tripled, from an average of 8% during 1997-2000 to 26% in 2001. Of the 10 U.S.-born drug-resistant cases reported in 2001, 8 (80%) were resistant to streptomycin (which was the only anti-TB drug to which five of those cases were resistant). Although streptomycin is the least commonly used of the five first-line anti-TB medications, this trend is concerning and without explanation. Of 56 persons with drug-resistant TB disease reported in 2001, 46 (82%) were born outside the U.S., including all four MDR-TB cases.
These and other TB surveillance data are available at www.health.state.mn.us/tb. The web site also includes TB-related educational brochures for patients in nine languages, national and state recommendations for TB screening and treatment, and other resources.
Yersiniosis is an acute bacterial enteric disease manifested by acute febrile diarrhea, acute mesenteric lymphadenitis which mimics appendicitis, septicemia, and many other symptoms. The cause is Yersinia enterocolitica and the reservoir is animals, particularly pigs. Transmission occurs by eating or drinking contaminated food and water or contact with infected animals. In Europe, infection is associated with eating raw pork; in the southern U.S., chitterlings are a common source.
We reviewed our surveillance data for the last 7 years (thank you ICPs and labs for your reports and isolates!); 175 cases were reported 1995-2001 with a mean number of 25 cases reported annually. Twenty-five percent of the cases were hospitalized; 3 persons had appendectomies. Y. enterocolitica comprises over 50 serotypes and 5 biotypes. We biotyped isolates in our lab and found 58% of clinical cases were associated with putative non-pathogenic types. Based on laboratory surveys we have conducted, a substantial proportion of labs do not routinely screen for Yersinia as part of their enteric screen. Thus, yersiniosis may be substantially underdiagnosed in Minnesota.
These data, as well as data on other emerging diseases, will be presented later this month at the International Conference on Emerging Infectious Diseases in Atlanta.
3. Chronic Wasting Disease
Chronic wasting disease (CWD) has been detected in samples of three Wisconsin deer that were shot during last November's hunting season. The three deer were from Iowa and Dane counties, near Madison. CWD is a transmissible spongioform encephalopathy (TSE), a fatal neurodegenerative disease. Other TSEs include bovine spongiform encephalopathy (mad cow disease) in cattle, and Creutzfeldt-Jakob disease in humans. CWD was first identified in Colorado in 1967 and is found in deer and elk in Colorado, Wyoming, and Nebraska. It has not been shown to be transmissible to humans or cattle. However, to be prudent, hunters should avoid eating the brain, spinal cord, eyes, tonsils, spleen or lymph nodes of white-tailed deer and elk, because the infectious agent (a prion) tends to concentrate in these tissues. (See previous Bug Bytes issues archived on our website for further discussion of TSEs and prions.) It is not known how the deer became infected in Wisconsin. The Minnesota Department of Natural Resources and the Board of Animal Health are reviewing surveillance efforts for CWD in Minnesota deer and farmed elk.
4. Meningococcemia Death
On March 6, an astute physician notified us of a death in a 4-year old with suspect meningococcal disease. The child presented with classical symptoms of Waterhouse-Friderichsen syndrome and expired shortly after admission. Immediate family and daycare contacts were recommended to receive chemoprophylaxis. Blood and cerebrospinal fluid collected before and after death have subsequently confirmed Neisseria meningitidis; serogrouping will be conducted in our lab.
Last year, there were 27 cases of meningococcal disease (a decrease from the usual 35-40) with 4 deaths; in 2002 to date there have been 7 cases with 2 deaths. Prompt reporting of cases to us allows us to provide advice regarding chemoprophylaxis, and to manage community anxiety and concerns.
Bug Bytes is a combined effort of the Infectious Disease Epidemiology, Prevention and Control Division and the Public Health Laboratory Division of MDH. We provide Bug Bytes as a way to say THANK YOU to the infection control professionals, laboratorians, local public health professionals, and health care providers who assist us.
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