Which one of the following diseases does not transmit through fine droplets coming out from mouth or nose of an infected person?

Correct — C, HIV-AIDS. HIV is a blood-borne and sexually transmitted virus. It moves through unprotected sexual contact, transfusion of infected blood or shared needles, and from an infected mother to her child during pregnancy, delivery or breastfeeding. It is not carried in the fine droplets expelled by coughing, sneezing or talking, and it does not survive outside the body long enough for that route to work. The other three diseases are all classic droplet infections.

• (a)Pneumonia — Pneumonia spreads through droplets carrying bacteria such as Streptococcus pneumoniae, or through viruses; it is a leading infectious cause of death in children under five.
• (b)COVID-19 — COVID-19 is caused by SARS-CoV-2 and spreads chiefly through respiratory droplets and aerosols released when an infected person breathes, speaks, coughs or sneezes. The 2021 exam was written during the pandemic.
• (d)Tuberculosis — Tuberculosis spreads through droplet nuclei carrying Mycobacterium tuberculosis, which stay suspended in the air of a poorly ventilated room; it is the textbook airborne bacterial infection.

Diseases are grouped by route of transmission, and the route decides the control measure. Droplet and airborne infections are answered with masks, ventilation, distancing and vaccination. Blood-borne and sexually transmitted infections are answered with screened blood supplies, sterile needles, barrier protection and treatment that suppresses the viral load. Mixing the two leads to controls that do not work and to stigma that does harm.

In 2021 this was a topical item, but the reasoning is permanent. HIV is fragile outside the body and needs direct entry into the bloodstream or mucosa, so it cannot travel on an exhaled droplet, share a cup or ride on a mosquito. Since the exam the wider position has moved: the World Health Organization ended the COVID-19 public health emergency of international concern on 5 May 2023, though the virus continues to circulate and tuberculosis remains India's larger burden of the two.

• HIV spreads through unprotected sexual contact, infected blood or blood products, shared needles, and mother-to-child transmission.
• HIV is not spread by respiratory droplets, casual contact, sharing utensils, or mosquito bites.
• Tuberculosis spreads by droplet nuclei carrying Mycobacterium tuberculosis and is the standard airborne bacterial infection.
• COVID-19 is caused by SARS-CoV-2 and spreads mainly through respiratory droplets and aerosols.
• The World Health Organization declared an end to the COVID-19 public health emergency of international concern on 5 May 2023.

• Assuming any infectious disease can spread by coughing.
• Believing HIV is spread by mosquitoes or by sharing food, both of which are false.
• Confusing the causative organism with the route of spread.

Set as a route-of-transmission odd-one-out, and topical in 2021; UPSC has asked the same content through a statement set on how AIDS is and is not transmitted.

• practice — not a real PYQ

  Which one of the following diseases is spread by droplet nuclei that remain suspended in indoor air?

  • (a)Malaria
  • (b)Tuberculosis
  • (c)Hepatitis B
  • (d)Typhoid

  Answer(b) Tuberculosis — malaria is vector-borne, hepatitis B blood-borne and typhoid water-borne.

• practice — not a real PYQ

  HIV can be transmitted by which one of the following?

  • (a)Sharing a meal with an infected person
  • (b)A mosquito bite
  • (c)Transfusion of infected blood
  • (d)Shaking hands

  Answer(c) Transfusion of infected blood — the virus needs direct entry into the bloodstream or mucosa.