Matthew E. Levison, MD, FACP

Diphtheria is a vaccine-preventable disease affecting mainly children. The primary immunization of three doses of the diphtheria toxoid in infancy is routine throughout the world, except where it isn’t. With proper childhood immunization and boosters, there should be little or no diphtheria. Although it is possible for immunized people to develop diphtheria, the disease is much less severe. In the unimmunized population, the mortality rate is 5% to 10%, and deaths occur mainly in the very young and the very old.

Neisseria meningitidis is a gram-negative diplococcus, which like all gram-negative bacteria, possesses a lipopolysaccharide-like component in its outer cell membrane. Almost all invasive isolates of N. meningitidis also express capsular polysaccharide. Based on the antigenic specificity of its capsular polysaccharide, meningococci are divided into 13 groups (A-E; H, I, K and L; and W-Z). However, most meningococcal infections worldwide are caused by only six of these 13 serogroups — A, B, C, W, X and Y.

Listeria monocytogenes is ubiquitous in the environment. It is a foodborne pathogen, but the infecting dose is unknown. Person-to-person transmission, other than from mother to fetus or directly to the newborn at the time of birth, is not believed to occur. With an incubation period of up to 2 months or more, it can be difficult to trace a food source; epid emiology is now being delineated with better investigative tools.

Nontuberculous mycobacteria, or NTM, also called mycobacteria other than tuberculosis, traditionally have been categorized by their rate of growth and pigment production in vitro using the Runyon classification. However, with the advent of genetic techniques, species-specific identification by sequencing a number of target genes, including the 16S ribosomal RNA gene, has led to many new species of NTM being described. Currently, there are more than 125 NTM species. NTM are classified into rapidly growing mycobacteria and slow growers.

Leprosy, also known as Hansen’s disease, is a chronic bacterial infection caused by Mycobacterium leprae, an obligate intracellular parasite. Although an ancient disease, leprosy continues to be a major health problem in the developing countries of Africa, Asia and Latin America. Several million people worldwide are permanently disabled by Hansen’s disease. Although 95% of the global total of new cases were reported from 14 countries in 2013 (Bangladesh, Brazil, Côte d’Ivoire, Democratic Republic of the Congo, Ethiopia, India, Indonesia, Madagascar, Myanmar, Nepal, Nigeria, Philippines, Sri Lanka and Tanzania), 59% were from India alone. In these countries, infected humans are the only known natural reservoir, and M. leprae are thought to spread person-to-person following long-term, close contact, usually with an infected member of the household who is excreting enormous numbers of leprosy bacilli in their nasal secretions. Nonetheless, only 5% of the world’s population are naturally susceptible to infection with M. leprae.

Once again our attention was drawn to Legionnaires’ disease this summer by a large outbreak in the South Bronx, New York, which involved more than 120 cases, including 12 deaths. The outbreak was attributed to a Legionella-contaminated hotel cooling tower. Other outbreaks this summer also occurred: in a different Bronx neighborhood soon thereafter, involving 13 cases and one death; in a Veterans home in Quincy, Illinois, involving 54 cases and 12 deaths; and in San Quentin State Prison in California, where more than 80 inmates became ill. According to the CDC, cases of Legionnaires’ disease have been increasing dramatically in the United States, with 2,270 in the first 7 months of 2014 and 2,472 cases in the same period this year, whereas only 1,500 cases were being reported annually 15 years ago. Does this represent a true surge in the number of cases of this disease, or is there something else going on?

Syphilis is currently epidemic among men who have sex with men in the United States and in many other parts of the world. Since 2000, rates of syphilis have been increasing in the U.S., as well as Canada, the United Kingdom, Australia and Europe, primarily among MSM. This is occurring despite more than 70 years of remarkable progress in control of this disease.

Lyme disease is here and doing well. It now is the most commonly reported vector-borne illness in the United States, with about 20,000 to almost 30,000 confirmed cases reported annually. In fact, the number may be considerably higher; the CDC estimates that the actual number of Lyme disease cases diagnosed annually may be as high as 300,000. Cases have been reported in every state in the last 10 years, with the exception of Hawaii. However, this disease is heavily concentrated in certain regions, with 96% of cases reported in 13 northeastern and north-central states [CDC. Lyme Disease Data. www.cdc.gov/lyme/stats/index.html (2014)], which correspond with the known geographic distribution of the Lyme disease vector Ixodes scapularis, the blacklegged or deer tick. Additional underreporting likely occurs in some highly endemic areas, like beach communities with transient summer residents, because diseases are reported by county of residence, rather than where the disease actually was acquired.

In the past 10 years, outbreaks or new mechanisms of spread have been seen with diseases never seen before in the United States. In some cases, this has occurred in diseases never before recognized anywhere in the world. Examples are the SARS (new disease), West Nile Virus, influenza A (H1N1) (new disease) and monkey pox outbreaks, as well as the anthrax attack (new method of spread). For this column, we are speculating on diseases that might emerge or spread in the United States in the next five to 10 years.