【Western medicine diagnotics question】CHP4 Infectious diseases, tropical medicine and sexually transmitted infection

CHP4 Infectious diseases, tropical medicine and sexually transmitted infection

1. Which haematogenous infections (bacterial, fungal and protozoal) can give rise to positive findings in the urine? What are the appropriate microbiological investigations for each infection?

Haematogenous infections seldom give rise to positive findings in the urine. However, infections such as infective endocarditis do produce red cells in the urine. On the whole, microbiological investigations of the urine are not useful in haematogenous infections.

2. Explain the term ‘zoonosis’.

A zoonosis is an infectious disease that has jumped from a non-human animal to humans. Zoonotic pathogens may be bacterial, viral or parasitic, or may involve unconventional agents and can spread to humans through direct contact or through food, water or the environment.

3. What are soil transmitters?

Hookworm, Ascaris, and whipworm are known as soil-transmitted helminths (parasitic worms). 

4. Explain the difference between bacteraemia and septicaemia. Can the presence of toxins, fungi or viruses in the blood also be called septicaemia?

Bacteremia is the simple presence of bacteria in the blood while Septicemia is the presence and multiplication of bacteria in the blood. Septicemia is also known as blood poisoning.

https://microbiologyinfo.com/differences-between-bacteremia-and-septicemia/

By definition, Septicemia implies that at least two of the following are abnormal:

● temperature (>38°C or <36°C)

● heart rate (>90 beats per min)

● respiratory rate (>20 /min or PaCO2 <4.3 kPa)

● white blood cell count (>12 or <4 × 109/L or >10% immature forms).

Septicemia has many causes; bacterial infection is the most common.

5. How is the safety of antibiotics used in pregnancy in different trimesters?

Antibiotics, like all drugs, should be avoided in pregnancy if possible. Co-trimoxazole is thought to be a teratogenic risk in the first trimester and produces neonatal haemolysis in the third trimester. Quinolones should also not be used in pregnancy. Whenever one is prescribing an antibiotic it is always wise to check local antibiotic policy, and this is even more so in pregnancy. Some drugs are not known to be harmful in pregnancy, e.g. penicillin.

6. What are the uses and the side-effects of the antibiotic lincomycin?

Lincomycin is an antibiotic that is used to treat severe bacterial infections in people who cannot use penicillin antibiotics. Lincomycin is used only for a severe infection. This medicine will not treat a viral infection such as the common cold or flu.

Antibiotic medicine can cause overgrowth of normally harmless bacteria in the intestines. This can lead to an infection that causes mild to severe diarrhea, even months after your last antibiotic dose. If left untreated this condition can lead to life-threatening intestinal problems.

Common side effects include:

• diarrhea, stomach pain;
• nausea, vomiting, swollen or painful tongue;
• vaginal itching or discharge;
• mild itching or rash;
• ringing in ears; or
• dizziness.

7. Is there any drug taken orally that prevents penicillin hypersensitivity reactions?

In the rare situation that no other antibiotic is available, steroid therapy would be the best measure to prevent hypersensitivity reactions. Penicillins, cephalosporins or any other beta-lactam antibiotic should not be used in patients with a history of penicillin allergy.

8. Is there any replacement intravenous antibiotic for those patients who have hypersensitivity to penicillin?

Yes, erythromycin is a good IV alternative, e.g. in severe respiratory

tract infections. Vancomycin is used IV in serious infections caused by Gram-positive bacteria. These are some examples but which antibiotic is used depends on the type of bacteria. Note that 10% of penicillinsensitive patients will also be allergic to cephalosporins.

9. Is it correct to perform an intradermal skin sensitivity test before administering penicillin or a cephalosporin?

There is no need to do skin testing without a history of penicillin allergy even if the drug is to be administered parenterally. 

10. Why are antibiotics not allowed in the treatment of rotaviruses?

Rotavirus is a virus and therefore is not sensitive to antibiotics, which are used for bacterial diseases.

11. Does aciclovir prevent the chances of developing herpes zoster (shingles) when given during primary infection?

Acyclovir works best when started within 48 hours of symptom onset. In herpes zoster (shingles) infections, acyclovir shortened the time it took lesions to scab over and decreased the time needed for the rash to heal and become pain-free. Adults older than 50 gained the most benefit from taking acyclovir.

12. How long does it take after vaccination to become immunized against chickenpox and therefore safe to work in infectious areas?

To ensure safety for healthcare workers in this situation, antibody levels should be checked 1–2 weeks post-vaccination.

13. Is meticillin-resistant Staphylococcus aureus (MRSA) the only major hospital-acquired infection?

No. Vancomycin-insensitive Staphylococcus aureus (VISA), vancomycinresistant Staphylococcus aureus (VRSA) and glycopeptide-resistant enterococci (GRE) are also problems. Clostridium difficile is another problem and occurs mainly after taking antibiotics.

14. Do you have to have antibiotics to get Clostridium difficile infection?

Usually. Clostridium difficile is normally carried by approximately 5% of the healthy population. It can cause diarrhoea after other normal bowel commensals have been eliminated by antibiotics. In addition, debilitated patients not on antibiotics can be infected by the faecal–oral route. Patients and healthcare workers can spread the organism through hand contact, hence the importance of hand washing.

15. Why do some patients with rheumatic fever later progress to chronic rheumatic heart disease?

Rheumatic fever, an inflammatory disease, can affect many connective tissues, especially in the heart, joints, skin, or brain. The infection often causes heart damage, particularly scarring of the heart valves, forcing the heart to work harder to pump blood.

16. What is the World Health Organization recommendation for the prophylaxis of rheumatic fever after a streptococcal throat infection?

The strategy to prevent additional streptococcal infection is to treat the patient with antibiotics over a long period of time. The antibiotic treatment that is most effective in preventing further infection is benzathine penicillin G, which is given by intramuscular injection every 3-4 weeks over many years.

17. Does rheumatic fever have an infectious or an immunological aetiology?

Both. Rheumatic fever starts with a streptococcal sore throat. It is followed by an immunological response, which is the result of molecular mimicry between the M proteins of the infecting Streptococcus pyogenes and cardiac myosin and laminin. This causes the cardiac lesions.

18. Why is migratory polyarthritis found in rheumatic heart disease?

Migratory polyarthritis found in rheumatic fever is due to the reaction of the circulating M protein of Streptococcus pyogenes and the synovial membrane. It is therefore migratory. There is no long-term damage to the joints.

19. Are penicillins still the drug of choice in streptococcal infections (particularly Strep. Pneumoniae)?

When administered at adequate dosage and frequency, penicillin remains the drug of choice for the treatment of pneumococcal pneumonia, despite the increasing prevalence of penicillin-resistant S. pneumoniae strains.

20. How long can the antistreptolysin-O (ASO) titre remain positive after a streptococcal infection?

The amount of ASO antibody (titer) peaks at about 3 to 5 weeks after the illness and then tapers off but may remain detectable for several months after the strep infection has resolved.

21. What is the effect of a suitable antibiotic on the ASO titre, if any?

Antibiotics have no effect on the levels.

22. What is the correct method of diagnosis of meningococcal septicaemia: cerebrospinal fluid culture or blood culture?

Blood culture for meningococcal septicaemia.

Note:

Meningococcal septicaemia

• Minutes count! Give IV penicillin immediately.
• Meningococcal vaccination: travellers to Saudi Arabia for the Hajj and Umrah pilgrimages must receive the polysaccharide vaccine (A, C, W 135 and Y serogroups).

23. Can Escherichia coli 0157 be spread by foods other than meats?

It is transmitted to humans primarily through consumption of contaminated foods, such as raw or undercooked ground meat products, raw milk, and contaminated raw vegetables and sprouts.

24. A patient with brucellosis in whom, after 6 weeks of treatment with 600 mg rifampicin +200 mg doxycycline, the agglutination test still shows a 1/320 titre. If, after stopping the treatment, the patient begins to experience identical symptoms as previously, how should treatment proceed? What is the best laboratory test to show relapse?

Significantly raised agglutination titres can remain for 2 years so these are not useful in diagnosing a relapse. Blood culture (positive in 50%) or polymerase chain reaction (PCR) should be used.

25. Do steroids have a role in the treatment of dengue haemorrhagic fever, in particular to prevent the further fall in the platelet count?

Two randomized, controlled trials (RCTs) in children have shown no benefit in children with dengue haemorrhagic fever. No effect was observed on bleeding episodes, other complications or mortality. Fluid replacement is vital.

26. Explain the mechanism of thrombocytopenia in dengue and malaria.

Dengue: platelet destruction due to virus/antibody immune complexes binding to the platelet surface. There is also a direct toxic effect on bone marrow.

Malaria: cytokine suppression of haemopoiesis.

27. What is the recommended procedure for the treatment of a case of dengue fever?

Mild cases need no active treatment. Dengue haemorrhagic fever requires urgent treatment, the key element being fluid replacement.

28. What diseases can you get from tick bites?

• Lyme Disease
• Anaplasmosis
• Babesiosis
• Ehrlichiosis
• Powassan Virus Disease
• Borrelia miyamotoi Disease
• Borrelia mayonii Disease
• Rocky Mountain Spotted Fever (RMSF)
• Tularemia

Further reading: https://www.health.state.mn.us/diseases/tickborne/diseases.html

29. Why has severe acute respiratory syndrome (SARS) not spread as widely as was predicted?

The reservoir includes civet cats, racoons, ferrets, badgers and animals that are sold in some Chinese food markets. Strict control of this practice has brought the epidemic under control. Bats are the likely host species.

30. Please explain the relation between recurrent typhoid fever and chronic carrier.

A chronic carrier is a patient who continues to carry the organism, usually in the gall bladder, for several months after clinical recovery. A ‘carrier’ implies no symptoms. A recurrence of disease occurs because of reinfection.

31. What is the single most confirmatory diagnostic test for typhoid?

Blood culture, which is positive in up to 80% of cases.

32. Has human-to-human transmission of the H5N1 avian influenza virus been described?

Human-to-human transmission is rare at the moment and most cases have been from transmission from birds and animals. The concern is that efficient transmission between humans will become substantial with changes in viral antigenicity. The 2009 H1N1 virus is a triple-reassortant virus with genes from human, swine and avian influenza viruses. Human-to-human transmission occurs with this virus.

33. In brucellosis, is it possible to see a brucella agglutination test of more than 1/160 even for years after specific and successful therapy of brucellosis?

Yes. Agglutination levels of 1/160 can persist for years. A four-fold rise in titre is needed to make a diagnosis of acute infection.

34. Please define the terms holoendemic, mesoendemic, and hyperendemic in relation to malaria.

These terms are defined in terms of the parasitaemia rate in adults or palpable spleen rates in children 2–9 years of age:

• Holoendemic: transmission occurs all year long. Greater than 75%
• Hyperendemic: intense, but with periods of no transmission during dry season. 50% to 75%
• Mesoendemic: regular seasonal transmission. 11% to 50%
• Hypoendemic: very intermittent transmission., less than 10%

35. You only recommend malarone for malarial prophylaxis when there is a significant chlorquine resistance. Isn’t malarone now widely used in travellers going to areas with low resistance.

Yes. The main problem with malarone is its expense. Remember, no drug is 100% effective. Always use insect repellents and insecticide-treated nets at night. Always check on the likelihood of chloroquine resistance in the country you are going to visit.

36. Parenteral vaccination with a killed suspension of Vibrio cholerae is recommended by some – isn’t an oral vaccine better?

Yes. Oral cholera vaccines should be used in conjunction with improvements in water and sanitation to control cholera outbreaks and for prevention in areas known to be high risk for cholera.

37. Is there a basis for treating patients for filariasis according to the eosinophil count (except for cases of tropical pulmonary eosinophils; TPE)? Filariasis is everywhere in my part of the world; a fluorescent antibody test (FAT) might not be very useful – except when there are very high values.

The definitive diagnosis is made by demonstrating microfilariae in the blood but absence does not exclude the disease. Eosinophilia is usually present during the acute phase of inflammation, so in the correct clinical context this could be used as a guide to treatment.

38. Why do patients who ingest eggs from a tapeworm in contaminated food not develop tapeworms?

To get tapeworms you need to ingest cystercera (not eggs), usually from eating undercooked pork. If you eat tapeworm eggs, as a result of faecal contamination of food, human cysticercosis might occur.

39. Why is a caesarean section recommended for the delivery of HIV-positive women?

HIV is shed into the cervical/vaginal birth canal as well as being present in the blood, which is why caesarean sections were used. However, with the use of highly active antiretroviral therapy (HAART) during pregnancy, the viral count is low and there is now no advantage in doing a caesarean section.

40. Why is HIV not transmitted when delivering a baby through caesarean section?

HIV is transmitted by blood and not usually by other fluids. There is very little contact between the baby and blood in a caesarean section.

41. Is HIV transmitted from mother to child during breastfeeding?
Is it possible to be infected with HIV through the ingestion of food and drinks contaminated with the virus?

Breast-feeding doubles the risk of mother-to-child transmission of HIV infection.

It is impossible to be infected with HIV through the ingestion of food and drinks contaminated with the virus.

42. Is it true that some patients are resistant to HIV infection despite repeated exposure to the virus?

Yes, it is true but only in a very few patients. One explanation is that mutations in the gene expressing the receptor for chemokine CCR5 might impair entry of HIV into cells and therefore confer some resistance to infection.

43. With regard to live vaccination and HIV, can MMR be given to an HIV-positive baby?

Yes, but not while the baby is severely immunosuppressed.

44. What are the causes of anaemia in HIV infection?

One of the most common causes is related to highly active antiretroviral therapy (HAART), e.g. megaloblastic anaemia, red call aplasia with zidovudine. Always remember to check drug therapy and side-effects. Other causes include anaemia of chronic disease and pancytopenia secondary to overwhelming opportunistic infection.

45. What are the measures necessary to prevent the transfusion of HIV-infected blood to an individual (please explain in light of the window period)?

In 2000, an assay for HIV RNA was introduced into blood-donor screening. HIV RNA appears earlier than p24 viral protein or HIV antibody. The window period is now thought to be 6–38 days. Transfusion of ‘window-period’ blood probably accounts for all HIV transmitted by transfusion in developed countries.

46. What is the recommended treatment for pulmonary anthrax?

Ciprofloxacin IV 400 mg twice daily. Untreated, the mortality rate is 90% and even in cases treated with ciprofloxacin for 60 days (in the USA) the mortality rate was still 45%.

47. What primary or specific tests should be performed before giving a patient primaquine for the treatment of relapsing malaria?

A test for glucose-6-phosphate activity should be performed before using primaquine as this drug can cause haemolysis in G6PD- deficient patients.

48. How sensitive is the polymerase chain reaction (PCR) test for herpes simplex virus 1 (HSV-1) in the cerebrospinal fluid (CSF) for confirming the diagnosis of HSV-1 encephalitis? And is herpes simplex virus 2 (HSV-2) usually tested for as well?

Sensitivity is 98% and specificity 94% for PCR. Both HSV-1 and HSV-2 are tested.

49. Herpes simplex is usually not associated with chronic infections such as tuberculosis or typhoid fever. Why is this?

This relates to the degree of immunosuppression. However, cases have been described where the patient has severe immunosuppression with decreased cellular immunity and tuberculosis and herpes simplex have occurred together.

50. Can scorpion bite be complicated by ischaemic stroke? If so, how does this occur?

Yes: the sting releases both catecholamines from the adrenal gland and acetylcholine from postganglionic parasympathetics. These have an effect on cerebral blood flow.