By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

Dr. Deresinski reports no financial relationships relevant to this field of study.

SYNOPSIS: CDC has updated the available information regarding reportable infectious diseases in the United States.

SOURCE: Adams DA, Thomas KR, Jajosky RA, et al. Summary of notifiable infectious diseases and conditions — United States, 2015. MMWR Morb Mortal Wkly Rep 2017;64:1-143.

CDC has provided an extensive report on notifiable infectious diseases in the United States for 2015. Their 143-page document is daunting to the reader, but, fortunately, the authors provide a section dealing with the highlights of the full report. What follows is a further summarization of selected infectious diseases.

VIRAL INFECTIONS

Arboviral Infections. A total of 2,175 cases of West Nile virus infections were reported in 2015, with 1,455 of these being neuroinvasive and 146 being fatal. California and Texas together accounted for 61% of cases. The incidence of neuroinvasive infections (0.45 cases per 100,000 population) was similar to the median incidence reported from 2002-2014.

Among domestically acquired arboviral infections, La Crosse virus infection was the second most frequently reported. This was followed by infections due to St. Louis encephalitis virus (all 23 cases of which were acquired in Arizona), Jamestown Canyon virus, Powassan virus, and Eastern equine encephalitis virus. The last is rare but fatal: Four of six patients with this infection died.

In the 50 states, one of the 896 cases of chikungunya infection was autochthonously acquired (in Texas). However, 237 infections were acquired in U.S. territories, including 227 in Puerto Rico and in the U.S. Virgin Islands.

In 2015, 951 laboratory-confirmed cases of dengue virus infection were reported in the United States, including its territories. Of those cases, 72% were travel-related, most frequently to the Caribbean and the Americas. An outbreak of 200 autochthonous cases occurred in Hawaii on Oahu, while the only other case acquired in a U.S. state was in Florida. The number of cases acquired in the endemic territories of Puerto Rico and the U.S. Virgin Islands was the lowest ever recorded.

Measles. Measles was officially declared to have been eliminated in the United States in 2000. Almost all (97%) cases are now import-associated, meaning that they are imported from abroad, epidemiologically linked to an imported case, or are caused by strains demonstrated by genetic methods to represent an imported genotype. Of the 150 reported cases in 2015, 80% were associated with six outbreaks, the largest of which involved 130 cases and was linked to two Disney theme parks. Cases from that outbreak were seen in seven additional states as well as in Mexico and Canada. Among the 150 cases in 2015, > 80% occurred in individuals who had not been vaccinated or whose vaccination status was unknown. Of note is that an immunocompromised adult with pneumonia died of undiagnosed measles virus infection.

Mumps. Eight outbreaks involving 20 cases accounted for 53% of the 1,329 cases of mumps reported in 2015; 88% of cases had been fully vaccinated. Seven (88%) of the outbreaks occurred in settings with high likelihood of close contact, including athletic teams, high schools, and universities.

Varicella. Since the change from the single-dose vaccination recommendation to two doses in 2015, the incidence of varicella has decreased 85% to 3.8 per 100,000. Among those for whom the information was available, 49% of cases occurred in children 1-9 years of age. Overall, among those with the relevant information, 58% had received at least one dose of vaccine and 57% of these had received a second dose. One-fifth of cases were associated with outbreaks. Five percent of cases resulted in hospitalization.

Influenza Virus Associated Pediatric Mortality. The median age of the 130 reported influenza-associated pediatric deaths in 2015 was 5.4 years (range, 27 days – 17 years). At least one pre-existing condition known to increase the risk of complications of influenza infection was present in 43%, with neurological disease in 18% of the total group. Positive bacterial cultures from normally sterile sites were obtained from 35 (48%) of 73 children, with Staphylococcus aureus recovered in 15 (43%) of 35. Twenty-seven (30%) of the 89 children 6 months of age had been fully vaccinated.

Rabies. Rabies caused two deaths in 2015. A 65-year-old man had been bitten by a dog while abroad, and a 77-year-old woman in Wyoming had a history of contact with a bat.

Human Immunodeficiency Virus (HIV) Infection. In 2015, 33,817 cases of newly diagnosed HIV infection were reported to the CDC, with blacks/African-Americans accounting for 44.5% and with an incidence of 37.7 per 100,000. The following states had incident diagnoses 15.0 per 100,000: District of Columbia, Florida, Louisiana, Maryland, Mississippi, New York, and South Carolina.

PROTOZOAN INFECTION

Babesiosis. Twenty-four states reported a total of 2,074 cases of babesiosis in 2015, with seven states (Connecticut, Massachusetts, Minnesota, New Jersey, New York, Rhode Island, and Wisconsin) accounting for 1,925 (93%).

Cryptosporidiosis. Cryptosporidium is the number one cause of waterborne outbreaks of infection, particularly of those related to recreational exposure to water. Adams and colleagues noted the following characteristics that contribute to this: A single bowel movement may release 108-109 infectious Cryptosporidium oocysts; oocysts may be shed for weeks; the infectious dose is only 10 oocysts; and the oocysts have a very high tolerance to chlorine.

Cyclosporiasis. Approximately one-third of reported cases of Cyclospora infection were associated with international travel. Fresh cilantro imported from Mexico was implicated as the vehicle in 61 restaurant-associated cases in Texas, Georgia, and Wisconsin.

PARASITIC

Trichinellosis. The known sources of the 13 cases of trichinellosis reported to the CDC were bear meat and pork. Two small outbreaks occurred both the result of eating meat from bears that had been hunted in Alaska.

FUNGAL

Coccidioidomycosis. There was a 36% increase in reported coccidioidomycosis cases in both California and Arizona, which recorded 3,053 and 7,622 cases, respectively. Separately, CDC has reported a dramatic increase in the number of cases in California to 5,372, with a comparably proportionate increase in incidence to 13.7 per 100,000 population.

RICKETTSIAL

Anaplasmosis and Ehrlichiosis. In 2015, 3,656 cases of anaplasmosis were reported in the United States an increase of approximately 31% over the previous year. In the mid-Atlantic states, there was a 70% increase. There was only a minimal increase in the number of cases of ehrlichiosis, with 1,475 due to Ehrlichia chaffeensis and 17 due to Ehrlichia ewingii.

BACTERIAL INFECTIONS AND INTOXICATIONS

Botulism. Of the 195 reported confirmed cases of botulism, 135 were instances of infant botulism, while 37 were foodborne and 20 were “other” (including wound botulism). Of the five identified outbreaks, the identified sources were potato salad, beets, and fermented seal flipper.

Shiga Toxin-producing Escherichia coli (STEC) Infection. While the overall incidence of STEC infections was 2.2 cases per 100,000 population, the incidence in children 1.4 years of age was almost four times higher at 8.0 per 100,000. The most serious complication of STEC infection is hemolytic uremic syndrome. This is associated most frequently with STEC O157, but other strains also may produce the toxin. As a consequence, it is recommended that stool specimens from individuals with community-onset diarrhea be tested routinely, not only by culture for the presence of STEC O157, but also by a method that detects either Shiga toxin itself or the gene that encodes it. This does not preclude the need for serogrouping and determination of the pulsed field gel electrophoresis pattern, both of which are important for epidemiological purposes.

Campylobacteriosis. It is estimated that Campylobacter causes 1.3 million illnesses in the United States each year and that most of these are the result of ingestion of domestic contaminated food. Furthermore, approximately 120 individuals die with this infection. Most cases are associated with ingestion of raw milk and undercooked chicken. A preliminary estimate of the incidence in 2015 is 17.7 cases per 100,000 population. Although most cases are sporadic, 35 outbreaks were reported with chicken liver pâté, grilled chicken, raw milk, and irrigation water among the implicated sources.

Cholera. Four of the five reported cases of cholera infection were associated with travel, including two cases related to travel to Haiti, and one each to Cuba and the Philippines. The non-travel case resulted from the ingestion of raw shrimp from the Philippines.

Shigellosis. Taking underdiagnosis into account, it is estimated that Shigella causes 500,000 symptomatic infections each year in the United States. During 2015, the incidence of reported cases of shigellosis in the United States was 7.3 per 100,000 population, with the highest incidence in children younger than 10 years of age. Although it may occur as the result of ingestion of contaminated food or water, Shigella infection most frequently is the result of person-to-person transmission. One group at increased risk is men who have sex with men.

The scourge of antibiotic resistance has reached Shigella, which caused several outbreaks due to multidrug-resistant strains. It is reported that, overall, 2.4% of isolates are resistant to ciprofloxacin, 4.7% to azithromycin, and that 15.3% were resistant to at least both ampicillin and trimethoprim-sulfamethoxazole. Susceptibility testing requires recovery of an isolate in culture so that use of non-culture methods alone is inadequate for management.

Reduced susceptibility of Shigella to ciprofloxacin was addressed in a recent CDC Health Advisory (https://emergency.cdc.gov/han/han00401.asp), which dealt with an increase in the number of isolates with an MIC of 0.12-1 mcg/mL or higher which, although within the susceptible range (the current CLSI breakpoint indicates that those with MICs 1 mcg/mL are susceptible), are significantly higher than that of most clinical isolates with usual MICs 0.015 mcg/mL. The isolates with an elevated MIC carry plasmid-related quinolone resistance genes that are not present in those with lower MICs. Although unproven, there is concern that treatment of these strains with a fluoroquinolone may result in reduced efficacy. When antibiotic therapy is indicated (most cases of shigellosis resolve quickly without antibiotic treatment), an alternative to ciprofloxacin should be chosen if the isolate has an MIC 0.12 mcg/mL, and the clinical laboratory should submit it to their public health laboratory.

Salmonellosis. There were 17.2 cases of Salmonella infection per 100,000 population in 2015, with the highest incidence in children < 5 years of age. The largest multistate outbreak was due to contaminated imported cucumbers. Some of the other sources included small turtles, pork, live poultry, and crested geckos.

Typhoid. Approximately four-fifths of the 367 cases of typhoid in 2015 were acquired in southern Asia, with visiting family and friends being the greatest risk factor. Overall, approximately 86% of cases were associated with international travel. There has been little change in the total annual number of cases since 2009.

Listeriosis. The incidence of reported Listeria monocytogenes infections in 2015 was 0.24 per 100,000 population. CDC has established an enhanced surveillance system, The Listeria Initiative, which uses molecular subtyping by pulsed-field gel electrophoresis and whole-genome sequencing for rapid outbreak investigations. Therefore, they recommend that all clinical isolates be submitted for evaluation. CDC indicates that this initiative has assisted in rapid identification of contaminated food sources, allowing them to be removed from the market, as in the case of the outbreak associated with Blue Bell ice cream.

Haemophilus influenzae Disease. The incidence of Haemophilus influenzae type B (Hib) infection in children in 2015 was 0.15 per 100,000, with a 99% decrease in those < 5 years of age since the introduction of conjugate Hib vaccines in 1987. However, the incidence among American Indian and Alaskan Native children is significantly higher than in other groups. Nontypeable strains now cause a majority of H. influenzae infections in all age groups.

Meningococcal Disease. The incidence of meningococcal disease, which was 0.12 per 100,000 population in 2015, remains at historic lows. However, the occurrence of outbreaks of infection due to Neisseria meningitidis serotype B on two college campuses resulted in nine cases, with one death. This and other recent experiences led to the Advisory Committee on Immunization Practices (ACIP) recommendation that meningococcal serotype B vaccine be administered to young adults 16-23 years of age as well as to certain groups at increased risk of infection and during outbreaks. Separately, CDC recently has warned of the high risk of development of meningococcal disease in individuals receiving eculizumab, despite prior vaccination.

Pertussis. The incidence of pertussis decreased from 10.3 to 6.5 per 100,000 population between 2014 and 2015, a reduction of 37.9%. One-third of cases occurred in those 11-19 years of age, a time of waning immunity. The highest incidence (67.2 per 100,000), however, was seen in infants < 1 year of age. Of the six deaths, three occurred in infants < 3 months of age and three occurred in adolescents with comorbid conditions. Two of the mothers of infants with fatal pertussis had not received Tdap at the recommended time (weeks 27-36) in pregnancy, while the vaccination status of the third was unknown.

Legionellosis. There continue to be yearly increases in the incidence of reported Legionella infection, reaching 1.89 cases per 100,000 population (6,079 cases). An outbreak involving 138 cases in the South Bronx was the largest community-associated outbreak since the one in Philadelphia in 1976. A consensus industry standard aimed at risk-reduction was published and is promoted by CDC.

Plague. Colorado and New Mexico each accounted for four of the 16 cases, Arizona and Oregon for two cases each, while California, Michigan, and Georgia had one case each. Four of the 16 cases of plague were fatal.

Brucellosis. The 126 cases of brucellosis were reported primarily from the South Atlantic, West South Central, and Pacific regions, which accounted for two-thirds. Physicians are encouraged to warn their clinical laboratories if they suspect brucellosis to reduce the risk of laboratory-acquired infection.

Tularemia. The 314 reported cases of tularemia in 2015 represent a 74% increase over the previous year. Eight states, led by Colorado (52 cases) and Kansas (34 cases), accounted for the majority of cases, with disproportionate increases in Colorado, Nebraska, South Dakota, and Wyoming states that apparently had had increases in rabbit populations.

SPIROCHETAL

Leptospirosis. Ninety-six cases of leptospirosis were reported from 10 states, jurisdictions, and territories, with 45 from Puerto Rico, 22 from Hawaii, and 11 from Guam.

MYCOBACTERIAL

Tuberculosis. The incidence of tuberculosis had remained largely unchanged at approximately 3.0 per 100,000 population from 2013-2015, but, compared to 2014, the number of cases increased by 1.6% to 9,557. Two-thirds of cases were foreign-born, with Asians accounting for almost one-half of this group. The incidence in Asians who were foreign-born was 18.2 per 100,000, which can be compared to 0.6 cases per 100,000 in non-Hispanic whites. Foreign-born individuals account for the majority of cases (total of 63 in 2015) of primary multidrug-resistant (MDR) TB, but the incidence in the general population has remained between 0.9% and 1.3% each year. Sixteen cases of extensively drug-resistant (XDR) TB have been reported since 2009.