Infectious diseases, tropical medicine and sexually transmitted infection

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4 Infectious diseases, tropical medicine and sexually transmitted infection

Questions

Question 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?

Question 2

Could you please explain the term ‘zoonosis’.

Question 3

What are soil transmitters?

Question 4

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

Question 5

I want to know about the safety of antibiotics used in pregnancy in different trimesters.

Question 6

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

Question 7

I have a question that keeps troubling me. Is there any drug taken orally that prevents penicillin hypersensitivity reactions?

Question 8

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

Question 9

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

Question 10

Why are antibiotics not allowed in the treatment of rotaviruses?

Question 11

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

Question 12

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

Question 13

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

Question 14

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

Question 15

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

Question 16

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

Question 17

Does rheumatic fever have an infectious or an immunological aetiology?

Question 18

Why is migratory polyarthritis found in rheumatic heart disease?

Question 19

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

Question 20

1. How long can the antistreptolysin-O (ASO) titre remain positive after a streptococcal infection?
2. What is the effect of a suitable antibiotic on the ASO titre, if any?

Question 21

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

Question 22

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

Question 23

I have a question about a patient with brucellosis in whom, after 6 weeks of treatment with 600mg rifampicin +200mg 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?

Question 24

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

Question 25

Please give me the mechanism of thrombocytopenia in dengue and malaria.

Question 26

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

Question 27

What diseases can you get from tick bites?

Question 28

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

Question 29

Please explain the relation between recurrent typhoid fever and chronic carrier, and the recommended treatment for both.

Question 30

What is the single most confirmatory diagnostic test for typhoid?

Question 31

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

Question 32

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?

Question 33

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

Question 34

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.

Question 35

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

Question 36

Please suggest possible reasons why Entamoeba histolytica infection associated with bloody diarrhoea is not relieved by treatment with ciprofloxacin and metronidazole 400mg × 2 daily over a 3-week period.

Question 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.

Question 38

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

Question 39

I have a query about one of the details in the book. You mention that perihepatitis is a feature of gonorrhoeal infection, but other books say that perihepatitis (Fitz-Hugh-Curtis syndrome) is a complication of chlamydial infections. Is there a possibility of perihepatitis in gonorrhoea? Thank you.

Question 40

In the 7th edition of Kumar and Clark Clinical Medicine, you indicate that there is no benefit in treating the male partner of a woman diagnosed with bacterial vaginosis (BV). As many physicians use the 2g × 1 metronidazole dose, is this unwarranted? Does it differ in women experiencing frequent recurrences of infection?

Question 41

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

Question 42

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

Question 43

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

Question 44

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

Question 45

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

Question 46

In a patient with meningitis: can the development of digital gangrene of the thumbs and sudden dyspnoea with a respiratory rate of 40/min, with intercostal, subcostal and suprasternal withdrawal, be attributed to disseminated intravascular coagulation (DIC)?

Question 47

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

Question 48

What is the recommended treatment for pulmonary anthrax?

Question 49

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

Question 50

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?

Question 51

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

Question 52

In my country, now that we know that the pin in the percussion reflex hammer bottom and the pinwheel can transmit infections such as hepatitis B from patient to patient, we prefer the use of wooden or dispersible metal pins. Do the authors agree?

Question 53

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

Answers

Answer 1

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.

Answer 2

Zoonoses are infections that can be transmitted from wild or domestic animals to man. Infections are acquired in various ways, e.g. direct contact (rabies from a dog bite), ingestion of animal products (campylobacter from chickens) and via an arthropod vector (tick bite, Lyme disease).

Answer 3

These are helminth infections and the main ones are ascariasis, trichuriasis and hookworm.

Answer 4

‘Bacteraemia’ means viable bacteria in the blood, e.g. viable bacteria can be found after tooth extraction. The term ‘septicaemia’ is difficult to define and is being replaced by ‘systemic inflammatory response syndrome’ (SIRS) (see K&C 7e, p. 899). By definition, this 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 <4.3kPa)
• white blood cell count (>12 or <4 × 109/L or >10% immature forms). SIRS has many causes; bacterial infection is the most common.

Answer 5

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.

Answer 6

Lincomycin is not available in the UK; its uses and side-effects are similar to those of clindamycin (see K&C 7e, p. 99). Its main use is in osteomyelitis because it is concentrated in bone.

Answer 7

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.

Answer 8

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 penicillin-sensitive patients will also be allergic to cephalosporins.

Answer 9

No, it is unhelpful.

Answer 10

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

Answer 11

There is no evidence that giving aciclovir during the primary infection (chicken pox) has any effect on the subsequent development of shingles.

Answer 12

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

Answer 13

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

Answer 14

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.

Answer 15

Antibodies to streptococcal polysaccharides are substantially elevated and can cross-react with some myocardial tissue antigens. The pathogenesis is, however, far from clear.

Answer 16

Phenoxymethylpenicillin 250 mg twice daily until the age of 20 years or for 5 years after the latest attack. This prevents recurrence and further cardiac damage.

Answer 17

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. Also, see next answer.

Answer 18

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.

Answer 19

Penicillin (usually amoxicillin) is the drug of choice for streptococcal infections. However, resistance to Streptococcus pneumoniae is increasing (up to 25% in some studies) and you should check your hospital’s antibiotic policy for the appropriate antibiotic.

Answer 20

1. The ASO titre peaks 4-5 weeks after infection. The levels then fall rapidly with a slower decline after 6 months.
2. Antibiotics have no effect on the levels.

Answer 21

Blood culture for meningococcal septicaemia. For treatment and vaccination see Box 4.1.

Box 4.1 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).

Answer 22

Yes. The reservoir for Escherichia coli 0157 is mainly the intestines of cattle. Thus, pasture land can become contaminated and organisms can be found on vegetables, e.g. sprouts and lettuce; unpasteurized milk is another source.

Answer 23

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.

Answer 24

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.

Further reading

Wills BD et al. (2005) Comparison of three fluid solutions for resuscitation in Dengue shock syndrome. New England Journal of Medicine353: 924.

Answer 25

• 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.

Answer 26

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

Further reading

Kumar P, Clark M (2009) Clinical Medicine, 7th edn, p. 115. Plus online appendix: http://www.studentconsult.com

Wills BA et al. (2005) Comparison of three fluid solutions for resuscitation in dengue shock syndrome. New England Journal of Medicine353: 877-889.

Answer 27

Lyme disease is well known in the West. Other diseases include tick-borne relapsing fever (Borrelia spp.), Rocky mountain spotted fever (Ricketssia ricketsii), Mediterranean spotted fever (R. conorii), Ehrlichosis (Ehrlichia spp.), babesiosis (Babesia spp.), and tick-borne encephalitis (virus).

Answer 28

SARS is due to a previously unknown coronavirus. 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.

Further reading

Guan Y et al. (2004) Molecular epidemiology of the novel corona virus that causes severe actue respiratory syndrome. Lancet363: 99-104.

Answer 29

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.

Answer 30

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

Answer 31

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.

Answer 32

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.

Answer 33

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

• hypoendemic is less than 10%
• mesoendemic 11-50%
• hyperendemic 51-75%
• holoendemic greater than 75%.

Answer 34

Yes, you are correct. 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.

Answer 35

Yes. Injectible cholera vaccine provides unreliable protection and is not available in UK. Oral vaccine containing inactivated Inaba strains (including El-Tor) and Ogawa strains is much better. However, this does not mean that precautions with the local drinking water should not be undertaken.

Answer 36

We can’t easily explain this; metronidazole is very effective in invasive amoebiasis. The most likely reason is that in this patient the diagnosis is wrong and you’re dealing with another cause of bloody diarrhea (e.g. inflammatory bowel disease) and the E. histolytica is present in the stool of your patient who is a carrier (i.e. not cause and effect). It may be E. dispar which is non-pathogenic.

Answer 37

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.

Answer 38

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.

Answer 39

Fitz-Hugh-Curtis syndrome was originally described as a complication of gonorrhoea infection, which still occurs. Chlamydia infection is now a much more common cause.

Answer 40

Placebo-controlled trials have shown that treatment of the male partner does not improve clinical outcome of treatment of BV or reduce recurrences. These trials included the use of metronidazole. The current guidelines do not recommend treatment of male partners. BV does seem to be acquired sexually so the reason for the lack of benefit of treatment is obscure.

Answer 41

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.

Answer 42

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.

Answer 43

1. Breast-feeding doubles the risk of mother-to-child transmission of HIV infection.
2. No.

Answer 44

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 (see K&C 7e, p. 185) might impair entry of HIV into cells and therefore confer some resistance to infection.

Answer 45

Yes, but not while the baby is severely immunosuppressed.

Answer 46

This sounds like meningococcal septicaemia, which can occur with meningococcal meningitis. It could be due to DIC, which certainly occurs, but the best clinical evidence of this is subcutaneous haemorrhages, gastric bleeding or bleeding from venepuncture sites.

Answer 47

1. 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.
2. 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.

Answer 48

Ciprofloxacin IV 400mg 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%.

Answer 49

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

Answer 50

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

Answer 51

This relates to the degree of immunosuppression. You are right; the diseases that you mention are not usually associated with herpes simplex. However, cases have been described where the patient has severe immunosuppression with decreased cellular immunity and tuberculosis and herpes simplex have occurred together.

Answer 52

Yes; use a broken ‘orange stick’.

Answer 53

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

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