12: INFECTIOUS DISEASES

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CHAPTER 12 INFECTIOUS DISEASES

WHOOPING COUGH

Whooping cough is now rare. After a catarrhal phase, it presents as an increasingly severe and paroxysmal cough. Send a nasopharyngeal swab for diagnosis. A differential white count shows a marked lymphocytosis. The treatment of pertussis is largely symptomatic. Erythromycin given for 10 days prevents spread of the illness. It should also be given to non-immunised child contacts (for pertussis vaccine, see p. 335). Admit if symptoms are severe (can cause apnoea in the very young).

Whooping cough is a notifiable disease.

MENINGITIS

There are 2000 cases per year of bacterial meningitis in the UK. Of these, 50% are due to Neisseria meningitidis. Viral meningitis is more common.

Diagnosis

Management

Any patient strongly suspected of having meningitis should be seen in hospital as soon as possible, even if there is a possible alternative explanation for the patient’s condition, e.g. otitis media.

The vast majority of pyrexial patients will be found on history and examination to have no features of meningitis, and most will have an obvious alternative diagnosis. Treat as appropriate. Take the opportunity to advise the patient or the parents of the features of meningitis.

Close family and school contacts should receive rifampicin 5 mg/kg 12-hourly for 2 days.

For suspected meningitis give benzylpenicillin im/iv 600 mg under 2 years of age, 1.2 g over 2 years, immediately, before arranging urgent hospital admission. If allergic to penicillin, give cefotaxime im/iv 50 mg/kg under 12 years of age, 1 g over 12 years.

Meningitis is a notifiable disease. The hospital should notify the Environmental Health Department.

SCARLET FEVER

Scarlet fever has become less common over the last 50 years. It is caused by a β-haemolytic Streptococcus, group A.

The incubation period is 2–4 days.

Management

Prescribe penicillin V 250–500 mg qds orally for 10 days, or erythromycin if the patient is allergic to penicillin.

Small epidemics of scarlet fever are sometimes seen.

GLANDULAR FEVER (INFECTIOUS MONONUCLEOSIS)

Glandular fever is an acute viral infection, mainly affecting teenagers, and is a common general practice problem.

The incubation period is usually 7–10 days, occasionally longer.

It can occur either sporadically or in epidemics.

Diagnosis

History.

• sore throat

• malaise or anorexia.

These are usually of a short duration, but the condition may present after several weeks of a combination of the above, with prolonged, intermittent symptoms. Upper abdominal pain indicates hepatitis or splenic enlargement.

Examination.

• tonsillar enlargement with exudate, which can be difficult to distinguish from bacterial or viral tonsillitis

• petechial haemorrhages on the soft palate

• posterior cervical lymphadenopathy

• hepatosplenomegaly

• maculopapular rash.

Investigations.

• An FBC and film will show a neutrophil leucocytosis of 10–20 × 10⁹/l.

• LFTs if jaundice is present.

• A Monospot/Paul Bunnell test will be positive in most cases of glandular fever, especially if taken at least 3 weeks after the start of the illness. False-negative results are common in the first week.

CHICKENPOX

Chickenpox is a common childhood illness in general practice, occurring usually in small epidemics.

The incubation period is 2–3 weeks.

After infection with chickenpox, the varicella-zoster virus remains dormant in dorsal root ganglia. Reactivation causes shingles (see p. 197).

Diagnosis

If the child is seen before the onset of the rash there may be a pyrexia and irritability. Otherwise the appearance of the rash is diagnostic.

Examination.

The rash starts with one or two maculopapular spots which are rapidly joined by many others. Vesicles develop from these as new spots appear. The rash is very itchy and in children scratch marks can often be seen. The whole body can be affected including the palms, soles, oral mucosa and scalp. In the final stage of the rash, after 5–10 days, the spots scab over.

Complications.

These are rare:

• chickenpox pneumonia (cough, wheeze and shortness of breath)

• encephalomyelitis (signs of meningism).

Management

• Paracetamol and calamine lotion are often all that are needed. Overheating tends to make the spots itch more. If impetigo develops in any of the spots, use fusidic acid ointment tds or oral flucloxacillin.

• In adults consider antiviral agent, e.g. aciclovir 800 mg five times daily for 7 days.

Is the patient immunocompromised or pregnant? If so, varicella zoster immunoglobulin may be needed (see p. 343).

INFLUENZA

Influenza commonly occurs as a winter and spring epidemic.

The incubation period is 24–48 hours.

PNEUMONIA

MALARIA

Malaria is becoming more prevalent in Britain with increased foreign travel. About 2000 cases occur every year in the UK, causing a dozen or so deaths.

Diagnosis

Examination.

Examination is often unhelpful in suggesting or confirming the diagnosis. Findings may include fever, jaundice and hepatomegaly.

Investigations.

Taking blood for a thick blood film for malarial parasites is essential in making the diagnosis. Send 5 ml of blood in a standard haematology tube and request a thick film for malaria. Mark the request urgent and ensure the results are available within 24 hours.

The result should identify the species of parasite.

If the result is negative, but the history strongly suggests the possibility of malaria, repeat the blood film at the height of the fever.

Management

If the diagnosis is confirmed or suspected, discuss the patient with the hospital medical team. An infectious diseases specialist is preferable, if available locally. Most cases are admitted, especially if the infection is due to Plasmodium falciparum.

Malaria is a notifiable disease.

Prevention

There are three important pieces of information to give to travellers about the prevention of malaria:

• Avoid being bitten, e.g. by using mosquito nets and insect repellents and wearing trousers and long-sleeved shirts in the evenings.

• Take antimalarial tablets as advised, making sure the course is completed (see below).

• Recognise the symptoms of malaria and seek medical help if suspicious: basically, report any febrile illness which occurs within 3 months of return from a malarious area.

Drug regimen.

The choice of antimalarial depends on the area visited, and the advice changes from time to time depending on local resistance of the Anopheles mosquito to chloroquine. For up-to-date advice, refer to the travel guides published regularly in the free GP magazines or ask the patient either to telephone the Medical Advisory Service for Travellers Abroad (MASTA) (see p. 357) or obtain online advice at www.preventingmalaria.info.

Whichever drugs are recommended, it is vitally important that they are started prior to travel and continued after leaving the malarious area.

Mefloquine should not be taken by patients with depression or other psychiatric disorders, any history of convulsions, or who are pregnant. The alternative antimalarials are less protective against malaria and the patient should reconsider the desirability of travelling to a malarious area.

CONJUNCTIVITIS

DIARRHOEA AND VOMITING

IMPETIGO

COLD SORES

Dry, cracked lips are common, especially during winter, and these can be treated with Vaseline. True herpes simplex (HSV-1) lesions are less common.

Diagnosis

History.

HSV-1 infection usually affects the lips, tongue, anterior buccal mucosa or nostrils. It is more common in children. It starts with painful ulcers or vesicles which form singly or in clusters and is often seen during another upper respiratory tract infection. The vesicles progress to crusts and often become secondarily infected, forming patches of impetigo (see p. 134).

Examination.

Confirms the above. If the patient presents at the impetigo stage it can be difficult to determine whether or not the underlying lesion is herpetic.

Investigations.

Herpes virus can be identified by electron microscopy of the vesicular fluid, but in practice this is rarely necessary.

Management

• Symptomatic treatment is often all that is necessary, with the use of analgesics, either orally or topically.

• Aciclovir is very effective in abating an attack of herpes, although its ability to eliminate the virus from the body is less certain.

• Aciclovir cream, 2 g, applied to the lesions five times a day, is usually sufficient if started at the first sign of an attack.

• For lesions inside the mouth, or if the vesicles are widespread in the mouth, valaciclovir tablets can be given 500 mg bd, or aciclovir suspension 200 mg (5 ml) five times daily over the age of 2 years, 100 mg (2.5 ml) five times daily under age 2 years.

• The total duration of treatment is 5 days.

SHINGLES

The rash of shingles is due to a reactivation of the chickenpox virus.

The incidence of shingles increases with age and is also more common in the immunocompromised.

It is mildly contagious, causing chickenpox, not shingles, in non-immune contacts. Shingles cannot be acquired by exposure to chickenpox.

Diagnosis

History.

The patient experiences tingling, paraesthesia or burning pain in the distribution of a single dermatome (see p. 353). This is followed 24 hours later by the appearance of the rash, starting with erythema, then maculopapular and vesicular lesions and progressing to pustules, crusts and, finally, scars.

Shingles is always unilateral. It is most likely to occur on the trunk, but the face is often affected.

Complications

• Secondary bacterial infection of the vesicles is common, indicated by yellow slough or crusts.

• If the rash is in the trigeminal nerve root distribution, look for spread to the eye or nose.

• Postherpetic neuralgia, i.e. continued pain after the rash has gone, may complicate shingles, especially in the elderly.

BOILS

The boil, or furuncle, is a common skin infection, occurring even in people with adequate hygiene.

Management

• Analgesia is often all that is required.

• Dress with magnesium sulphate paste under an absorbent dressing if the boil looks ready to discharge.

• Prescribe flucloxacillin 250 mg qds for 5 days if the surrounding skin is erythematous or if lymphangitis is present.

• If the boil is very tense and painful, relief may be gained by incising it through its pointing head with the tip of a scalpel blade, after spraying the boil with e.g. ethyl chloride. The boil can be gently squeezed to massage pus out and a dry dressing applied.

• If the patient is found to be a carrier of Staphylococcus, prescribe Naseptin cream, oral flucloxacillin and an antiseptic shower soap for 2 weeks.

HEPATITIS

Hepatitis A is the most common form of hepatitis seen in general practice in the UK. The incubation period is about 1 month. Infection spreads by the faecal–oral route, or by ingestion of infected food.

Hepatitis B is acquired parenterally, e.g. by blood transfusion, needlestick injury or sexually.

Prior to 1991, hepatitis C in the UK was usually caused by infected blood transfusion. Since the introduction of screening blood donors, the commonest cause of hepatitis C has been intravenous drug misuse. It is not easily spread through sexual contact.

Diagnosis

Examination

• Jaundice is most evident in the sclerae.

• Lymphadenopathy and splenomegaly may be present.

• The liver is usually tender but not palpable.

• The urine tests positive for bilirubin, even in anicteric cases.

Investigations

• LFTs: show a raised AST and bilirubin.

• FBC: shows a lymphocytosis.

• Hepatitis viral screen: anti-HAV IgM shows a rising titre over 7–10 days in acute hepatitis A.

• Prothrombin time should remain normal. (A rising prothrombin time indicates hepatic failure.)

• Hepatitis B surface antigen is diagnostic of acute hepatitis B. Five to ten per cent of patients go on to develop chronic hepatitis. In these the surface antigen remains positive. If they are also e-antigen positive, they remain highly infectious.

• Antibodies to hepatitis C appear relatively late in the course of the disease. If clinical suspicion is high, test for hepatitis C virus RNA to establish the diagnosis.

Management

• No specific treatment is needed for hepatitis A or B.

• Bed rest is initially advisable, with simple analgesics for muscle or abdominal pains.

• The acute illness usually resolves in 3–6 weeks.

• A full, well-balanced diet and adequate fluid intake are recommended.

• Monitor for signs of fulminant hepatic failure (confusion, disordered LFTs).

• In hepatitis B and C warn the patient of possible spread to sexual contacts.

• Offer hepatitis B immunisation to family members and sexual contacts.

• Patients testing positive for hepatitis C should be referred for consideration for interferon alfa to reduce the risk of chronic infection.

• In acute hepatitis B check for hepatitis B surface antigen at 3 months. Only about 5–10% remain positive in the UK. All such patients should be referred for expert follow-up.

• For immunisation, see pp. 341–342.

General malaise for 2–3 months is common. Alcohol should be avoided for 6 months. Oral contraceptives can be resumed after clinical and biochemical recovery.

Viral hepatitis is a notifiable disease. Isolation is not necessary, but good personal hygiene is advisable to prevent the spread of infection. Children can return to school as soon as clinical recovery allows.

HIV/AIDS

Over 53 000 people in the UK are estimated to be HIV-positive, with about 6600 new cases per year. The main sources of transmission are sexual and through blood-to-blood contact. All persons who are sexually active should be advised on the prevention of HIV and AIDS. Safe- and low-risk sex should be promoted (see p. 2).

Increasing numbers of patients are requesting HIV testing in the wake of a growing public awareness of the disease and its risk factors. HIV testing is only performed with the patient’s consent.

Not all GPs feel able to provide appropriate counselling. Genitourinary medicine clinics can.

The test must be performed at least 3 months after the at-risk exposure, as this is considered to be the time taken for seroconversion to occur.

The follow-up appointment

• If the result is negative, the patient did not have antibodies to HIV at the time of the test. A further test is indicated if there has been possible exposure to the virus within the previous 3 months.

• Reiterate the advice on safe sex and needle use.

• Most HIV-positive people remain asymptomatic for many years. Patients have now survived over 20 years with HIV, and new drugs are being developed and used which delay the progression of the disease. There were fewer than 500 deaths from AIDS in the UK in 2003. (See: breaking bad news, p. 316.)

• Arrange further follow up in the GUM clinic.

HIV-positive patients

Patients with HIV-positive status should be followed up regularly in a GUM or specialist HIV clinic.

The GP should consider the HIV-positive patient to be immunocompromised, i.e. any pyrexial illness should be treated seriously. Patients with a low T4 count should be admitted.

Chest infections may be due to Pneumocystis jiroveci (formerly P. carinii). Tuberculosis is also not uncommon.

Close liaison with the patient’s consultant is essential. There is a greater need to consider confidentiality as a sensitive issue in many cases of HIV disease.

PYREXIA OF UNKNOWN ORIGIN (PUO)

In theory, PUO is a pyrexia greater than 38°C, lasting more than 3 weeks, with no known cause after extensive investigation.

In general practice, thorough investigation is not possible. Many patients present with a temperature, and in some of these the cause will not be found with any great certainty. It is, however, rare in general practice for a genuine pyrexia to last more than 2 weeks.

Examination.

• clubbing, splinter haemorrhages, joint effusions, rashes

• ear, nose and throat infections

• cervical lymphadenopathy

• chest infection

• heart murmurs

• organomegaly.

Management

Most persistent fevers can be diagnosed following a thorough history, examination and the above simple investigations. In the absence of a diagnosis, referral to an infectious diseases specialist is warranted if the pyrexia has lasted for more than 3 weeks.

The blind use of antibiotics is to be avoided in prolonged pyrexia. Refer for diagnosis first.

WEIL’S DISEASE

Weil’s disease is the rare form of leptospirosis with jaundice that is usually caught from infected rat’s urine and therefore affects mainly sewage workers, water board workers and people who swim in contaminated rivers.

Management

In mild cases without jaundice it may be difficult to distinguish Weil’s disease from a flu-like illness.

Jaundiced patients with a history of a biphasic febrile illness, headache, severe muscle pains and possible exposure to rat’s urine should be admitted for investigation and intravenous antibiotic treatment of suspected Weil’s disease.

The mortality in jaundiced patients is 10%.

LYME DISEASE

Lyme disease is a flu-like illness characterised by the rash of erythema migrans. It is caused by the spirochete, Borrelia burgdorferi, and is transmitted by tick bite, usually from deer ticks in areas such as the New Forest.

Management

• Discuss the case with the infectious diseases department.

• Outpatient treatment is usually possible, with oral antibiotics such as amoxicillin 500 mg tds for 10–14 days or doxycycline 100 mg bd for 10–14 days.

• Most features of the disease respond well, especially if treated early.

• Complications include arthritis, Bell’s palsy, heart block and lymphocytic meningitis. These are rare.

MEASLES

Measles is now uncommon in Britain due to the high uptake of the MMR vaccine and, previously, measles vaccines. Measles is more common towards the end of the year.

The incubation period is 2 weeks.

Management

• There is no specific treatment for uncomplicated measles.

• Secondary bacterial infections should respond to the appropriate antibiotic.

• Human normal immunoglobulin is advisable for immunocompromised patients.

• For childhood immunisation against measles, see p. 338.

Measles is a notifiable disease.

MUMPS

Mumps is becoming increasingly rare following the introduction of the MMR vaccine. It is most common in school-age children and young adults.

The incubation period is 18–21 days.

RUBELLA

Rubella is becoming increasingly rare with the widespread use of the MMR vaccine.

The incubation period is 2.5–3 weeks.

Diagnosis

History.

Rubella is often a mild illness characterised by conjunctival suffusion and rhinitis, followed, after 24 hours, by a discrete, light pink maculopapular rash.

Examination.

Examination confirms the features in the history. Also present are enlarged lymph nodes in the postauricular and suboccipital groups.

Investigations.

Investigations are unnecessary except in pregnant women without proven immunity who are in contact with a suspicious rash. Send 10 ml of clotted blood to the virology laboratory for haemagglutination and IgM titres. Repeat serology may be requested after 10 days.

Differential diagnosis.

The commonest confusion is with roseola infantum and non-specific viral rashes. Rubella is unusual without a certain amount of lymphadenopathy, which is often lacking in the non-specific illnesses.

Complications.

Complications are very unusual. Joint pain is probably the most common.

Management

• Symptomatic treatment is usually all that is required. The rash should last no longer than 5 days.

• Refer for foetal assessment if blood tests suggest an acute infection in pregnancy.

• For immunisation, see p. 338.

Rubella is a notifiable disease.

Related

Churchills Pocketbook of General Practice