What are the recommended laboratory tests for a 5-year-old child presenting with fever after returning from Mexico?

From the Guidelines

For a 5-year-old returning from Mexico with fever, I strongly recommend a comprehensive diagnostic approach including complete blood count (CBC) with differential, blood cultures, malaria thick and thin smears, dengue serology (IgM and IgG), comprehensive metabolic panel, urinalysis, and stool examination for ova and parasites, as these tests are crucial in identifying the underlying cause of fever in a traveler returning from an area with endemic vector-borne diseases 1. The choice of lab tests is guided by the clinical presentation and the epidemiology of infectious diseases in the region visited. Given that Mexico has areas endemic for diseases like dengue, Zika, and malaria, testing for these conditions is essential.

• A CBC with differential can help differentiate between bacterial and viral infections, which is critical in guiding antibiotic use and reducing the risk of antibiotic resistance.
• Blood cultures are necessary to detect bacteremia, which can be life-threatening if not promptly treated.
• Malaria testing, including thick and thin smears, is crucial due to the high morbidity and mortality associated with malaria if left untreated or inadequately treated 1.
• Dengue serology (IgM and IgG) and tests for other vector-borne diseases like Zika and chikungunya should be considered based on the specific regions visited within Mexico and the clinical presentation of the patient.
• A comprehensive metabolic panel and urinalysis can provide insights into the patient's hydration status, renal function, and potential electrolyte imbalances, all of which are important in managing fever and potential infections.
• Stool examination for ova and parasites is important as it can identify pathogens causing traveler's diarrhea, which may present with fever even in the absence of prominent gastrointestinal symptoms. Considering the potential for respiratory infections, especially in a child, influenza testing and a respiratory viral panel should be included if respiratory symptoms are present, as these can help guide specific antiviral treatment and reduce the inappropriate use of antibiotics 1. The child's vaccination history and specific travel locations within Mexico should be taken into account when interpreting test results, as these factors can influence the risk of certain infections and the likelihood of specific vaccine-preventable diseases. Empiric treatment should not be initiated before obtaining these diagnostic specimens unless the child appears critically ill, as this approach helps ensure that treatment is targeted and effective, reducing the risk of morbidity and mortality associated with untreated or inadequately treated infections.

From the Research

Recommended Lab Tests

For a 5-year-old returning from Mexico with fever, the following lab tests are recommended:

• Complete Blood Count (CBC) to check for abnormalities in blood cell counts, such as thrombocytopenia, which is common in malaria and other arboviral infections 2
• C-reactive protein (CRP) test to assess the severity of infection and differentiate between malaria and other infections 2
• White Blood Cell (WBC) histogram to detect abnormal peaks, which can indicate the presence of certain arboviruses 2
• Multiplex real-time RT-PCR assay to simultaneously detect Zika, chikungunya, dengue, yellow fever, West Nile, and Japanese encephalitis viruses 3
• Malaria diagnostic tests, such as rapid diagnostic tests (RDTs) or microscopy, to detect Plasmodium species 2, 4

Considerations

When interpreting lab results, consider the following:

• The patient's travel history and exposure to mosquitoes in Mexico, which increases the risk of arboviral infections 5, 6, 4
• The clinical presentation and symptoms, such as fever, headache, and rash, which can be similar across different arboviral infections 5, 4
• The importance of differential diagnosis to rule out other potential causes of fever, such as bacterial or viral infections 5, 4

Additional Tests

Depending on the patient's clinical presentation and lab results, additional tests may be necessary, such as:

• Liver function tests to assess for hepatitis or other liver damage 4
• Renal function tests to assess for kidney damage or dysfunction 4
• Imaging studies, such as ultrasound or CT scans, to evaluate for complications or other conditions 4