Enterococcus is a gram-positive coccus that resides in the intestinal tract and the environment. It is isolated from stool cultures of healthy individuals and may also contaminate urine samples. Examples of the enterococcal species involved in human infections include E. faecalis, E. faecium, E. gallinarum, and E. casseliflavus, and approximately 70% of the enterococci isolated from clinical specimens are E. faecalis. Enterococci are opportunistic pathogens that cause infections, such as bacteremia, endocarditis, and urinary tract and abdomen/pelvis infections in immunocompromised hosts (e.g., older adults; those with diabetes, malignant tumors, or heart disease; and post-operative patients). Bacteremia and endocarditis are particularly serious, and bacteremia caused by E. faecium has a high case-fatality rate. Vancomycin is an extremely important antibacterial drug for infections caused by enterococci that are naturally resistant to cephems, carbapenems, and aminoglycosides.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative virus of coronavirus disease 2019 (COVID-19), is classified into the family Coronaviridae, genus Betacoronavirus, and has a positive-sense, single-stranded RNA genome consisting of approximately 30,000 bases. SARS-CoV-2 uses angiotensin-converting enzyme 2 (ACE2) as a receptor to attach to and enter human cells. SARS-CoV-2 is an enveloped virus and is inactivated by alcohol, detergents, etc.
Pertussis is defined as an “acute respiratory tract infection caused by Bordetella pertussis (B. pertussis) ” in the reporting criteria for physicians under the Infectious Diseases Control Law. The main symptom is prolonged coughing and the severity is greater in infected newborns or infants. In Japan, the “adsorbed diphtheria-purified pertussis-tetanus combined (DPT) vaccine” has been used in routine immunization, but in November 2012, DPT-IPV, consisting of DPT and inactivated polio combined vaccine (IPV), was introduced as a routine immunization. According to the immunization schedule for DPT-IPV in Japan, for the primary series, three subcutaneous injections are administered (usually for those 3-12 months of age) with an interval of at least 20 days between each dose (the standard interval is 20-56 days). For the booster dose, after the initial dose a subcutaneous injection is administered at least 6 months after three doses of the primary series (the standard interval is 12-18 months after completion of three doses of the primary series). Immunity acquired by vaccination wanes in 3-4 years, and those previously vaccinated may also become infected and develop the disease. In developed countries, adolescents and adults being a source of infection, transmitting the disease to their families and unvaccinated children, sometimes resulting in severe illness, is of concern (see pp. 111&112 of this issue). As one of the measures to protect infants from pertussis, some countries recommend vaccination of adolescents and adults, including pregnant women, with a reduced quantity of pertussis and diphtheria antigens in DPT (Tdap; not approved in Japan) (IASR 40: 14-15, 2019). In Japan, DPT can be vaccinated on a voluntary basis instead of Tdap.
Enterohemorrhagic Escherichia coli (EHEC) infection is caused by E. coli that produces Verotoxin/Shiga toxin (VT/Stx) and/or possesses VT-encoding genes. The main signs/symptoms of EHEC infections are abdominal pain, watery diarrhea, and bloody diarrhea. Vomiting and/or fever (≥38°C) are occasionally observed. VT-producing EHEC can cause hemolytic uremic syndrome (HUS), which involves thrombocytopenia, hemolytic anemia, and acute kidney injury; complications, such as encephalopathy, may also occur, with potentially fatal outcomes.
Human mastadenoviruses (Ad), which belong to the genus Mastadenovirus in the family Adenoviridae, are non-enveloped double-stranded DNA viruses that are relatively physicochemically stable. Ads are currently grouped into seven species from A to G and over 80 types have been described (as an example, type 3 is denoted as Ad3). Ads have been reported as serotypes up to Ad51, but those classified after Ad52 have been reported as genotypes based on whole genome sequencing.
The genus Acinetobacter comprises glucose non-fermentative, Gram-negative, rod-shaped bacteria that cause opportunistic infections. Acinetobacter species can cause pneumonia and other respiratory tract infections, urinary tract infections, infections at sites of surgery or trauma, catheter-related bloodstream infections, sepsis, and other conditions in immunocompromised patients and others.
(IASR Vol. 42 p27-28: February 2021)
Coronavirus disease 2019 (COVID-19), which first occurred in Wuhan, China in December 2019, spread worldwide in a short period of time and was declared to be in a pandemic state by the World Health Organization (WHO) on March 11, 2020. According to the Johns Hopkins University COVID-19 Dashboard dated January 4, 2021, a cumulative total of 85,136,586 cases and 1,843,342 deaths were reported from 191 countries and territories (see p.29 of this issue).
(IASR Vol. 42 p1-2: January 2021)
Acute hepatitis C is caused by infection of the hepatitis C virus (HCV), which belongs to the Flaviviridae family, genus Hepacivirus. After a latency period of 15-160 days (average 7 weeks), acute hepatitis develops with multiple symptoms such as general fatigue, cold-like symptoms, anorexia, chills, nausea, or vomiting; in 30-40% of patients, the virus becomes undetectable and the patient is cured, but the remaining 60-70% become HCV carriers and often progress from acute to chronic hepatitis. Asymptomatic carriers infected with HCV who have no symptoms account for 20-30% of HCV-infected individuals. The probability of spontaneous remission from chronic hepatitis is very low, at approximately 0.2%, and 10-16% of patients are thought to develop cirrhosis after an average of 20 years after the initial infection. Moreover, patients with cirrhosis develop hepatocellular carcinoma at a high rate of greater than 5% per year. The total number of deaths due to liver cancer used to exceed 30,000 a year, but has been on a downward trend since around 2000 (Cancer statistics in Japan, National Cancer Center, 1958-2018). The HCV carrier rate has also decreased since 2000 (see p.3 of this issue). Hepatitis C cases are diagnosed mostly via the combination of anti-HCV antibody and quantification of HCV RNA. Since 2014, direct acting antivirals (DAAs) have been used instead of interferon, which has problems with effectiveness and side effects; more than 95% of treated patients achieve sustained virological response (SVR), i.e., undetectable HCV RNA in the blood, 24 weeks after the end of the treatment (see p.5 of this issue).
(IASR Vol. 41 p211-212: December 2020)
Exanthema subitum (ES) is a febrile exanthematous disease in infancy with a generally good prognosis, characterized by a fever that lasts about three days and exanthema with fever reduction. In the acute phase, loose stool/diarrhea, bulging anterior fontanel, eyelid edema, and occipital lymphadenopathy are observed. Mottled exanthema on both sides of the uvula, so-called Nagayama’s spots, may appear in the early phase of the disease.
(IASR Vol. 41 p191-193: November 2020)
The 2019/20 influenza season (from week 36 in September 2019 to week 35 in August 2020) was characterized by the predominance of the influenza A/H1pdm09 subtype, and influenza B, mainly Victoria lineage, also increased from week 51 in 2019.