Microbiology - NCLEX-PN

Rhinovirus, a type of picornavirus, is implicated in up to 50-80% of cases of the common cold. Other less common causes include human coronavirus (15% of cases), influenza (10%), and adenovirus (5%).

The majority of infectious vomiting and diarrhea in infants and young children is viral in origin, with the most commonly implicated virus being rotavirus. Norovirus is another common cause of viral gastroenteritis in individuals of all ages, though it is not as common in young children as rotavirus.

In most children and adults, Zika virus causes a mild fever characterized by myalgia, fatigue, and headache. The population most at risk for serious complications from the disease is unborn fetuses. Exposure to Zika virus before birth has been associated with microcephaly, a frequently fatal disorder of abnormal skull and brain development.

Zika virus is primarily transmitted via mosquito bite. However, it can also be transmitted by sexual contact and it can cross the placenta, allowing an infected mother to pass the virus to an unborn child.

Koplik's spots are oral lesions seen early-on in infection with the measles virus. These spots are only present in a minority of cases, though. Other common symptoms of measles include high fever (often over 104 degrees fahrenheit), cough, runny nose, and a maculopapular rash which begins at the hair line and spreads down to the trunk and extremities.

The most noticeable symptom in mumps infection is enlargement of the parotid glands, while Epstein Barr infection can result in fatigue, lymphadenopathy, and hepatosplenomegaly. Scarlet fever is not a viral infection, but rather is caused by the bacteria streptococcus pyogenes.

The measles virus is one of the most highly contagious of all childhood exanthems. It is spread primarily by respiratory droplets, or by touching a surface that has been in contact with an infected individual's saliva or mucus. It is not spread in feces, nor is it blood or vector borne.

Measles, while generally only a moderately severe disease, is fatal in one out of every 500 children who contract the virus.

Genital herpes is most frequently associated with herpes simplex virus 2 (HSV2), while herpes simplex virus 1 (HSV1) has been associated more often with oral herpes (cold sores). However, new evidence suggests that both viruses can live in either location: HSV1 can spread to the genitals and cause genital herpes, while HSV2 can be spread to the oral mucosa to cause cold sores.

An infection of the finger, toe, or cuticle with the herpes simplex virus is known as a herpetic whitlow. This infection causes painful swelling and erythema at the site of contact and is often caused by the finger coming into contact with a cold sore (oral herpes simplex lesion). It is more common in individuals who are frequently in contact with oral mucosa, such as dentists and dental hygienist, nurses, and in individuals who bite their nails or suck their fingers or thumb.

The most common cause of infectious hearing loss in neonates is cytomegalovirus (CMV), also known as human herpes virus 5. While this disease rarely causes symptoms in adults, it can cause significant harm to a fetus. One of the primary fetal consequences of CMV infection in pregnancy is hearing loss. Other issues can include vision loss, developmental delays, and seizures.

All of the other infections listed can have significant impacts on the health of a fetus or neonate, including pre-term birth, spontaneous abortion, and vision loss, though none are currently associated with risk of hearing loss.

In adult populations, cytomegalovirus poses the greatest risk to immunocompromised individuals, such as people on immunosuppressive drugs or in HIV patients who have developed AIDS. In pregnant people, CMV generally does not pose a risk to the mother, but rather to the fetus. Athletes and teens that are not immunocompromised often will have mild or unnoticeable symptoms when infected with CMV.

Human papillomavirus, herpes simplex virus, and hepatitis B virus are a sexually-transmitted viruses with double-stranded DNA genomes. While herpes simplex virus has a relatively large genome, the genome of both human papillomavirus and hepatitis B virus are both quite small.

Candida albicans is a fungus present in the normal flora of humans. An overgrowth of this fungus may cause yeast infections of the skin, vagina, or mouth. After a child receives antibiotics, they may contract a mycotic diaper rash due to Candida albicans overgrowth since the normal bacterial flora have been eliminated by the antibiotics. Pneumocystis jirovecii may cause pneumocystis pneumonia. Blastomyces dermatitidis and Aspergillus fumigatus may cause lung infection if the spores are inhaled. Lastly, Sporothrix schenckii may cause a skin infection called Sporotrichosis after it enters through a break in skin integrity.

Prions are infectious protein particles that affect proteins, misfolding them and causing loss of function. They are most commonly found in the brain. Prion diseases are also called transmissible spongiform encephalopathies (TSEs) and include diseases such as mad cow disease and Creutzfeldt-Jakob disease.

The TB skin test has different thresholds for positive values based on the size of induration. In an HIV-positive individual (low CD4+, immunocompromised), a test is considered positive if it is > 5 mm (not cm). A positive result takes 24 to 48 hours to reveal itself.

The two most common bacterial arrangements are Staph- and Strep-. Staph- is a non-symmetrical arrangement like a cluster of grapes. Strep- indicates a chain of bacteria.

The three most common bacterial shapes are listed below.

Coccus—round or oval

Bacillus—rectangular or rod-shaped

Spirilla (spirochete)—spiral

By breaking down names into arrangement and shape, students can predict or identify the appearance of an organism by its name. In the example Staph indicates arrangement in a chain. Coccus indicates round or oval in shape. Therefore, Staphylococci are round or oval-shaped organisms arranged in a cluster.

Bordetella pertussis is a Gram negative, rod-shaped aerobe. It requires oxygen to function and commonly infects the respiratory tract of young children, causing whooping cough.

Neisseria gonorrhoeae is a Gram negative coccus bacterium that generally presents as a diplococcus (in pairs of cocci).

_Staphyloccocus aureus are Gram positive cocci. Chlamydia trachomatis and Rikettsia prowazekii are both classified as Gram negative rods and Neisseria meningitidis are Gram negative cocci.